path: root/Documentation/user-manual.txt

// Subsurface 4.1 User Manual
// ==========================
// :author: Manual authors: Jacco van Koll, Dirk Hohndel, Reinout Hoornweg,
// Linus Torvalds, Miika Turkia, Amit Chaudhuri, Jan Schubert, Willem
// Ferguson, Salvador Cuñat
// :revnumber: 4.1
// :revdate: May 2014
:icons:
:toc:
:toc-placement: manual
:numbered:
// :website: http://subsurface.hohndel.org

image::images/Subsurface4Banner.png["Banner",align="center"]

[big]#USER MANUAL#

*Manual authors*: Willem Ferguson, Jacco van Koll, Dirk Hohndel, Reinout Hoornweg,
Linus Torvalds, Miika Turkia, Amit Chaudhuri, Jan Schubert, Salvador Cuñat

[blue]#_Version 4.1,  May 2014_#


Welcome as a user of _Subsurface_, an advanced dive logging programme with
extensive infrastructure to describe, organise, interpret and print scuba
and free dives. _Subsurface_ offers many advantages above other similar
software solutions:

 - Do you use two different dive computer brands, each with its own proprietary
   software for downloading dive logs? Do you dive with rebreathers as well
   as open circuit? Do you use a Reefnet Sensus time-depth recorder
   in conjunction with a dive computer? _Subsurface_ offers a standard
   interface for downloading dive logs from all these different pieces of
   equipment and to store and analyse the dive logs within a unified system.
 - Do you use more than one operating system? _Subsurface_ is fully compatible
   with Mac, Linux and Microsoft, allowing you to access your dive log on each
   of your operating systems in a unified way.
 - Do you use Linux or Mac and your dive computer has only Microsoft-based software
   for downloading dive information (e.g. Mares)? _Subsurface_ provides a way of
   storing and analysing your dive logs on other operating systems.

_Subsurface_ binaries are available for Windows PCs (Win XP or later), Intel
based Macs (OS/X) and many Linux distributions. _Subsurface_ can be built for
many more hardware platforms and software environments where Qt and
libdivecomputer are available.

The scope of this document is the use of the _Subsurface_ program. To install
the software, consult the _Downloads_ page on the
http://subsurface.hohndel.org/[_Subsurface_ web site].
Please discuss issues with this program by sending an email to
mailto:subsurface@hohndel.org[our mailing list] and report bugs at
http://trac.hohndel.org[our bugtracker].  For instructions on how to build the
software and (if needed) its dependencies please consult the INSTALL file
included with the source code.

*Audience*: Recreational Scuba Divers, Free Divers, Tec Divers, Professional
Divers

toc::[]

[[S_StartUsing]]
Start Using the Program
-----------------------

The _Subsurface_ window is usually divided into four panels with a *Main
Menu* (File Import Log View Filter Help) at the top of the window (for Windows
and Linux) or the top of the screen (for Mac and Ubuntu Unity). The four panels are:

1. The *Dive List* to the bottom left containing a list of all the dives in the
user's
dive log. A dive can be selected and highlighted on the dive list by clicking on
it. In most situations the up/down keys can be used to switch
between dives. The Dive List is an important tool for manipulating a dive log.

2. The *Dive Map* to the bottom right, showing the user's dive sites on a world
map
and centred on the site of the last dive selected in the *Dive List*.

3. The *Dive Info* to the top left, giving more detailed information on the
dive selected in the *Dive List*, including some statistics for the selected dive or for all
highlighted dive(s).

4. The *Dive Profile* to the top right, showing a graphical dive profile of the
selected dive in the *Dive List*.

The dividers can be dragged between panels in order to change the size of any of
the panels. _Subsurface_ remembers the position of the dividers, so the next
time _Subsurface_ starts it uses the positions of the dividers when the program
was executed previously.

If a dive is selected in the *Dive List*, the dive location, detailed information
and profile of
the _selected dive_ are shown in the respective panels. On the other hand, if
one highlights more than one dive the last highlighted dive is the _selected
dive_, but summary data of all _highlighted dives_ are shown in the *Stats* tab
of the *Dive Info* panel (maximum, minimum and average depths, durations, water
temperatures and SAC; total time and number of dives selected).

[[S_ViewPanels]]

image::images/main_window.jpg["The Main Window",align="center"]

The user can determine which of the four panels are displayed by selecting the
*View* option on the main menu. This feature gives the user several choices of
display:

*All*: show all four of the panels as in the screenshot above.

*Divelist*: Show only the Dive List.

*Profile*: Show only the Dive Profile of the selected dive.

*Info*: Show only the Dive Notes about the last selected dive and statistics for
all highlighted dives.

*Globe*: Show only the world map, centred on the last selected dive.

Like many other functions that can be accessed via the Main Menu, these options
can be triggered using keyboard shortcuts. The shortcuts for a
particular system
are shown with an underline in the main menu entries. Since different Operating
Systems and the user chosen language may cause _Subsurface_ to use different
shortcut keys they are not listed here in the user manual.

When the program is started for the first time, it shows no information at all.
This is because the program doesn't have any dive information available. In the
following sections, the procedures to create a new logbook will be described.

[[S_NewLogbook]]
Creating a new logbook
----------------------
Select _File -> New Logbook_ from the main menu. All existing dive data are
cleared so that new information can be added. If there are unsaved data in an
open logbook, the user is asked whether the open logbook should be
saved before a new logbook is created.

[[S_GetInformation]]
== How to store dive information in the user's logbook

There are several ways in which dive information can be added to a logbook:

1. Enter dive information by hand. This is typically useful if the diver did not
use a dive computer and dives were recorded in a written logbook.

2. Import dive information directly from a dive computer if it is supported by
_Subsurface_. The latest list of dive computers supported by _Subsurface_ can
be found at:
link:http://subsurface.hohndel.org/documentation/supported-dive-computers/[
Supported dive computers].

3. Import dive information from another data base or file format. This is
discussed in more detail below.

[[S_EnterData]]
=== Entering dive information by hand

This is usually the approach for dives without a dive computer. The basic record
of information within _Subsurface_ is a dive. The most important information
in a simple dive logbook usually includes dive type, date, time, duration,
depth, the names of your dive buddy and of the dive master or dive guide, and
some remarks about the dive. _Subsurface_ can store much more information
than this for each dive. In order to add a dive to a dive log, select _Log
-> Add Dive_ from the Main Menu. The program then shows three panels to enter
information for a dive: two tabs in the *Info* panel (*Dive Notes* and
*Equipment*), as well as the *profile* panel that displays a graphical profile
of each dive. These panels are respectively marked [red]#A#, [red]#B# and
[red]#C#
in the figure below. Each of these tabs will now be explained for data entry.

image::images/AddDive1.jpg["FIGURE: Add dive",align="center"]

==== Dive Notes

This panel contains the date, time and place information for a particular dive,
environmental conditions, co-divers and buddies, as well as some descriptive
information. The message in a blue box at the top of the panel indicates that
the dive is being edited. If one clicks on the *Dive Notes* tab, the following
fields are visible:

image::images/AddDive2.jpg["FIGURE: The Dive Notes tab",align="center"]

The *Start time* field reflects the date and the time of the dive. By clicking
the down-arrow on the right of that field a calendar will be displayed from
which
one can choose the correct date. The time values (hour and minutes) can also be
edited directly by clicking on each of them in the text box and by overtyping the
information displayed.

*Air and water temperatures*: the air and water temperatures during the
dive can be typed directly on the fields to the right of the Start time.
Temperature units are not needed, as they will be automatically supplied by
_Subsurface_. Only the numerical value must be
typed by the user (The units selected in the 'Preferences'
will determine whether metric or imperial units are used).

*Location*: Here the name of the dive site can be entered, e.g. "Tihany, Lake
Balaton,
Hungary". Auto completion of location names will make this easier if one
frequently dives at the same sites.

*Coordinates*: The geographic coordinates of the dive site should be entered
here. These can come from three sources:

a. One can find the coordinates on the world map in the bottom right hand
part
of the Subsurface window. The map displays a green bar indicating "No location
data - Move the map and double-click to set the dive location". Upon a double-click
at the appropriate place, the green bar disappears and the coordinates are
stored.

b. The coordinates can be obtained from the _Subsurface_ Companion app if the
user has an Android device with GPS and if the coordinates of the dive site
were stored using that device.
xref:S_Companion[Click here for more information]

c. The coordinates can be entered by hand if they are known, using one of
four formats with latitude followed by longitude:

	ISO 6709 Annex D format e.g. 30°13'28.9"N 30°49'1.5"E
	Degrees and decimal minutes, e.g. N30° 13.49760' , E30° 49.30788'
	Degrees minutes seconds, e.g. N30° 13' 29.8" , E30° 49' 1.5"
	Decimal degrees, e.g. 30.22496 , 30.821798

Southern hemisphere latitudes are given with a *S*, e.g. S30°, or with a
negative value, e.g. -30.22496. Similarly western longitudes are given with a
*W*, e.g. W07°, or with a negative value, e.g. -7.34323.

Please note that GPS coordinates of a dive site are linked to the Location
name - so adding coordinates to dives that does not have a location description
will cause unexpected behavior (Subsurface will think that all of these
dives have the same location and try to keep their GPS coordinates the
same.

*Divemaster*: The name of the dive master or dive guide for this dive can be
entered here.
Again, this field offers auto completion based on the list of dive masters in
the current logbook.

*Buddy*: In this field one can enter the name(s) of the buddy / buddies
(separated by commas) who accompanied the user on the dive. Auto completion
is offered based on the list of buddies in the current logbook.

*Suit*: The type of diving suit used for the dive can be entered here.
As with the other items, auto completion of the suit description is available.

*Rating*: In this field, provide a subjective overall rating of the
dive on a 5-point scale by clicking the appropriate star on the rating scale.

*Visibility*: As with the previous item, provide a rating of
visibility during the dive on a 5-point scale by clicking the appropriate star.

*Tags*: Tags that describe the type of dive performed may
be entered here (separated by commas). Examples of common tags are boat, drift,
training, cave etc. _Subsurface_ has many built-in tags. Auto completion is once again offered.
For instance, if, for instance, +cav+ was typed, then the tags *cave* and *cavern* are
shown for the user to choose from.

*Notes*: Any additional information can be typed here.

The *Save* and *Cancel* buttons are used to save all the information for tabs in
the info panel and in the dive profile panel, so there's no need to use them
until ALL other information has been added. Here is an example of a completed
Dive Notes panel:

image::images/CompletedDiveInfo.jpg["FIGURE: A completed Dive Notes tab",align="center"]

==== Equipment

The Equipment tab allows the user to enter information about the type of
cylinder and gas used, as well as the weights used for a dive. The message in a
blue
box at the top of the panel:

image::images/BlueEditBar.jpg["Blue edit bar",align="center"]

indicates that the dive is being edited. This is a highly interactive part of
_Subsurface_ and the information on
cylinders and gases (entered here) affects the behaviour of the dive profile
(top right-hand panel).

[[S_CylinderData]]
*Cylinders*: The cylinder information is entered through a dialogue that looks
like this:

image::images/CylinderDataEntry1.jpg["FIGURE:Initial cylinder dialogue",align="center"]

The + button at the top right allows the user to add more cylinders for this
dive.
The dark dustbin icon on the left allows one to delete information for a
particular cylinder.

Start by selecting a cylinder type on the left-hand side of the
table.  To select a cylinder, click in the *Type* box.
This brings up a button that can be used to display a dropdown list of
cylinders:

image::images/CylinderDataEntry2.jpg["FIGURE:The cylinder drop-down list button",align="center"]

The drop-down list can be used to select the cylinder type used
for the dive or the user may start typing in the box which shows the
available options for the entered characters. The
*Size* of the cylinder as well as its working pressure (*WorkPress*) will
automatically be shown in the dialogue. If a cylinder is not shown in the dropdown list, type the name and description of that cylinder into the *Type* field.

Next, indicate the starting pressure and the ending pressure of
the
gas used during the dive. The unit of pressure (metric/imperial) corresponds
to the setting in the _Preferences_.

Finally, type in the gas mixture used in the *O2%* field. If air
was used, a value of 21% can be entered on this field,  or it might be
left blank. If nitrox or trimix were used, their percentages of oxygen and/or
helium must be specified.
Any inappropriate fields should be left empty. After typing the information for
the cylinder, press _ENTER_ on the keyboard or click
outside the cell that contains the cursor. Information for any additional
cylinders can be added by using the + button at the top right hand. Following
is an example of a complete description for a
dive made using two cylinders (air and EAN50):

image::images/CylinderDataEntry3.jpg["FIGURE: a completed cylinder dive information table",align="center"]

*Weights*: Information about the weight system used during a dive can be entered
using a dialogue very similar to that for the cylinder information. If the user
clicks the + button on the top right of the weights dialogue, the table looks
like this:

image::images/WeightsDataEntry1.jpg["FIGURE: The Weights dialogue",align="center"]

If one then clicks on the *Type* field, a drop-down list becomes accessible
through a down-arrow:

image::images/WeightsDataEntry2.jpg["FIGURE: Weights type drop-down list button",align="center"]

The drop-down list can then be used to select the type of weight system or the user may start
typing in the box which shows the available options for the entered characters. In
the *Weight*
field, the weight used during the dive must be typed. After typing the
information
for the weight system the user must either press _ENTER_ on the keyboard or
click outside the
cell that contains the cursor. It is possible to enter
information for more than one weight system by adding an additional system using
the + button on the top right hand. Weight systems can be deleted using the
dustbin icon on the left hand. Here is an example of information for a dive
with two types of weights: integrated and a weight belt:

image::images/WeightsDataEntry3.jpg["FIGURE: A completed weights information table",align="center"]

There's NO need to click the _Save_ button before the dive
profile has been completed.

[[S_CreateProfile]]
==== Creating a Dive Profile

The *Dive Profile* (a graphical representation of the depth of the dive as a
function of time) is indicated in the panel on the top right hand of the
_Subsurface_ window. When a dive is manually added to a logbook, _Subsurface_
presents a default dive profile that needs to be modified to best represent the
dive being described:

image::images/DiveProfile1.jpg["FIGURE: Initial dive profile",align="center"]

_Modifying the dive profile_: When the cursor is moved around the dive profile,
its position is indicated by two colored lines (red and green) as shown below.
The depth and time
that the cursor represents are indicated, respectively on the left hand and
bottom axes. The units (metric/imperial) on the axes are determined by the
*Preference* settings. The dive profile itself comprises several
line segments demarcated by waypoints (white dots on the profile, as shown
above). The default dive depth is 15 m.
If the dive depth was 21 m then the user needs to drag the appropriate waypoints
downwards to represent 21 m. To add a waypoint, double-click on
any line segment. To move an additional waypoint, drag it.
To remove this waypoint, right-click on it and choose "Remove this point" from the
context menu. The user needs to drag the waypoints to represent an
accurate
time duration for the dive. Below is a dive profile that represents a dive
to 21 m for 31 min, followed by a 5 minute safety stop at 5 m.

image::images/DiveProfile2.jpg["FIGURE: Edited dive profile",align="center"]

_Specifying the gas composition:_ The gas composition used is clearly indicated
along the line segments of the dive profile. This defaults to the first gas
mixture specified in the *Equipment* tab, which was air in the case of the
profile illustrated above. The gas mixtures of segments of the dive profile can
be edited. This is done by right-clicking on the particular
waypoint and selecting the appropriate gas from the context menu. Changing
the gas for a waypoint affects the gas shown in the segment _to the left_ of
that
waypoint. Note that only the gases defined in the *Equipment* tab appear in the
context menu.

image::images/DiveProfile3.jpg["FIGURE: Gas composition context menu",align="center"]

Below is the profile of a dive to 21 m for 31 min for which an extra waypoint was added at 18 m on the ascent and with a switch from air to
EAN50 at 18 m. In this case the first cylinder in the *Equipment* tab
contained air and the second cylinder contained EAN50.

image::images/DiveProfile4.jpg["FIGURE: Completed dive profile",align="center"]

==== Saving the hand-entered dive information

The information entered in the *Dive Notes* tab, the *Equipment* tab as well as
the *Dive Profile* can now be saved in the user's logbook by using the two
buttons
on the top right hand of the Dive Notes tab. If the _Save_ button is clicked,
the dive data
are saved in the current logbook. If the _Cancel_ button is clicked, the newly
entered
dive data are discarded. When exiting _Subsurface_, the user will be prompted
once more to save the logbook with the new dive(s).


[[S_ImportDiveComputer]]
=== Importing new dive information from a Dive Computer

==== Connecting and importing data from a dive computer.

The use of dive computers allows the collection of a large amount of
information about
each dive, e.g. a detailed record of depth, duration, rates of ascent/descent
and of gas partial pressures. _Subsurface_ can capture this information and
present it as part of the dive information, using dive
information from a wide range of dive computers. The latest list of supported
dive computers can be found at:
link:http://subsurface.hohndel.org/documentation/supported-dive-computers/[
Supported dive computers].

[icon="images/icons/warning2.png"]
[WARNING]
Several dive computers consume more power when they are in their
PC-Communication mode. **This could drain the dive computer's battery**. We
therefore
recommend that the user checks if the dive computer is charged when
connected to the USB port of a PC. For example, several Suunto and Mares dive
computers do not recharge through the USB connection. Users should refer to
the dive computer's manual
if they are unsure whether the dive computer recharges its batteries
while connected to the USB port.

To import dive information from a dive computer to a computer with
_Subsurface_,
it is necessary that the two pieces of equipment communicate with one another.
This
involves setting up the communications port (or mount point) of the computer
with _Subsurface_ that communicates with the dive computer. In order to set up
this communication, one needs to find the appropriate information to
instruct
_Subsurface_ where and how to import the dive information.
xref:_appendix_a_operating_system_specific_information_for_importing_dive_information_from_a_dive_computer[Appendix A]
provides the technical information to help the user achieving this for different
operating
systems and
xref:_appendix_b_dive_computer_specific_information_for_importing_dive_information[Appendix B]
has dive computer specific information.

After this, the dive computer can be hooked up to the user's PC, which can be
achieved by following these steps:

1. The interface cable should be connected to a free USB port (or the Infrared
	or Bluetooth connection set up as described later in this manual)

2. The dive computer should be placed into PC Communication mode.
	(Users should refer to the manual of their specific dive computer)

3. In _Subsurface_, from the Main Menu, the user must select _Import -> Import
From Dive Computer_.
Dialogue *A* in the figure below appears:


image::images/ImportFromDC1.jpg["FIGURE: Download dialogue 1",align="center"]

Dive computers tend to keep a certain number of dives in their memory, even
though these dives have already been imported to _Subsurface_. For that reason
_Subsurface_ only imports dives that have not been uploaded before. This makes
the download process faster on most dive computers and also saves battery power
of the dive computer (at least for those not charging while connected via USB).
If, for some reason, the user wishes to import ALL dives from the dive computer,
even though some may already be in the logbook, then check the check box labeled
_Force download of all dives_.

 - The dialogue has two drop-down lists, *Vendor* and *Dive Computer*. On the
*vendor* drop-down list select the make of the computer, e.g.
Suunto, Oceanic,
Uwatec, Mares. On the *Dive Computer* drop-down list, the model name of
the dive computer must be selected, e.g. D4 (Suunto), Veo200 (Oceanic), or Puck
(Mares).

 - The *Device or Mount Point* drop-down list contains the USB or Bluetooth port
name that _Subsurface_ needs in order to communicate with the dive computer.
The appropriate port name must be selected. Consult
xref:_appendix_a_operating_system_specific_information_for_importing_dive_information_from_a_dive_computer[Appendix A]
and
xref:_appendix_b_dive_computer_specific_information_for_importing_dive_information[Appendix B]
for technical details on how to find the appropriate port information for a
particular dive
computer and, in some cases, how to do the correct settings to the operating
system of the computer on which _Subsurface_ is running.

 - If all the dives on the dive computer need to be downloaded, check the
   checkbox _Force download of all dives_. Normally, _Subsurface_ only downloads
   dives after the date-time of the last dive in the *Dive List* panel. If one
   or more of your dives in _Subsurface_ have been accidentally deleted or if there
   are older dives that still need to be downloaded from the dive computer, this
   checkbox needs to be activated. Some dive computers (e.g. Mares Puck) do not provide
   a contents list to _Subsurface_ before the download in order to select only new dives.
   Consequently, for these dive computers, all dives are downloaded
   irrespective of the status of this check box.

 - If the checkbox _Always prefer downloaded dives_
   has been checked and, during download, dives with identical date-times exist on
   the dive computer and on the _Subsurface_
   *Dive List* panel, the record in the _Subsurface_ divelog will be overwritten
   by the record from the dive computer

 -  Do *not* check the checkboxes labeled _Save libdivecomputer logfile_ and
    _Save libdivecomputer dumpfile_. These are only used as diagnostic tools
    when problems with downloads are experienced (see below).

 -  The _OK_ button must then be clicked. Dialogue *B* in the figure above
appears.

 - With communication established, one can see how the data are
retrieved from the dive computer.
Depending on the make of the dive computer and/or number of recorded dives, this
could take some time. The user should be patient. The _Download_ dialogue
shows a
progress bar at the bottom of the dialogue (for some dive computers the
progress information could be inaccurate as we cannot determine how much
downloadable data there is until all data have been downloaded). When the
download of the dive information is complete, all the imported dives appear
in the *Dive List*, sorted by date and time. Disconnect and
switch off the dive
computer to conserve its battery power.
If a particular dive is selected, the *Dive Profile* panel shows an informative
graph of dive depth against time for that particular dive.


 - If there is a problem in communicating with the dive computer, an error
message will be shown, similar to this text: "Unable to open /dev/ttyUSB0 Mares
(Puck Pro)". Refer to the text in the box below.


****
*PROBLEMS WITH DATA DOWNLOAD FROM A DIVE COMPUTER?*
[icon="images/icons/important.png"]
[IMPORTANT]
Check the following:

 - Is the dive computer still in PC-communication or
Upload mode?

 - Is the battery of the dive computer fully charged? If not then the battery
must be charged or replaced.

 - Is the connecting cable faulty? Does the cable work perfectly using other
software? Has it worked before, or is this the first time the cable is being used?

 - Consult
xref:_appendix_a_operating_system_specific_information_for_importing_dive_information_from_a_dive_computer[Appendix A]
and make sure that the correct Mount Point
was specified (see above).

 - On Unix-like operating systems, does the user have write permission to the
USB port? If not, consult
xref:_appendix_a_operating_system_specific_information_for_importing_dive_information_from_a_dive_computer[Appendix A]

If the _Subsurface_ computer does not recognise the USB adaptor by
showing an appropriate device name next to the Mount Point, then there is a
possibility that the cable or USB adaptor is faulty. A faulty cable is the most
common cause of communication failure between dive computer and _Subsurface_
computer. It is also possible that the _Subsurface_ computer cannot interpret
the data. Perform a download for diagnostic purposes with the following
two check boxes checked in the download dialogue discussed above:

	Save libdivecomputer logfile
	Save libdivecomputer dumpfile

*Important*: These check boxes are only used when problems are encountered
during the download process: under normal circumstances they should not be checked.
When checking these boxes, the user is prompted to select a folder to
save the information to. The default folder is the one in which the _Subsurface_
dive log is kept.

*Important:* _After downloading with the above checkboxes
checked, no dives are added to the
*Dive List* but two files are created in the folder selected above_:

	subsurface.log
	subsurface.bin

These files should be send to the _Subsurface_ mail list:
_subsurface@hohndel.org_ with a
request for the files to be analysed. Provide the dive computer
make and model
as well as contextual information about the dives recorded on the dive computer.
****


[[S_EditDiveInfo]]
==== Updating the dive information imported from the dive computer.

The information from the dive computer is not complete and more
details must be added in order to have a more full record of the dives. To
do this,
the *Dive Notes* and the *Equipment* tabs on the top left hand of the
_Subsurface_ window should be used.

==== Dive Notes

The date and time of the dive, gas mixture and (often) water temperature is
shown as obtained from the dive computer, but the user needs to add some
additional information by hand in order to have a more complete dive record.
The message in a blue box at
the top of the panel indicates that the dive is being edited. If the user
clicks on the *Dive Notes* tab, the following fields are
visible:

image::images/AddDive3.jpg["FIGURE: The Dive Notes tab",align="center"]

The *Start time* field reflects the date and the time of the dive, as supplied by
the dive computer. It should therefore not be necessary to edit this, but one
could make changes by clicking the down-arrow on the right of that field to
display a calendar from which the correct date can be chosen. The hour and
minutes values can also be edited by clicking on each of them in the text box
and by overtyping the information displayed.

*Air/water temperatures*: Air and water temperatures during the dive are shown
in these fields to the right of the Start time. Many dive computers supply water
temperature information and this field may therefore not require further
editing. If
editing is required, only a value is required. The units of temperature will be
automatically supplied by
_Subsurface_ (according to the _Preferences_, metric or imperial units will
be used).

*Location*: In this field one should type in text that describes the site
where the dive was performed, e.g. "Tihany, Lake Balaton, Hungary".
Auto completion of location names will
make this easier when a user frequently dives at the same sites.

*Coordinates*: The geographic coordinates of the dive site should be entered
here. These can come from three sources:

a. The user can find the coordinates on the world map in the bottom right hand
part
of the Subsurface window. The map displays a green bar indicating "Move the map
and double-click to set the dive location". Double-click
at the appropriate place, the green bar disappears and the coordinates are
stored.

b. The user can obtain the coordinates from the _Subsurface_ Companion app if
an Android device with GPS was used and the if the coordinates of the dive site
were stored using that device.
xref:S_Companion[Click here for more information]

c. The coordinates can be entered by hand if they are known, using one of
four formats with latitude followed by longitude:

	ISO 6709 Annex D format e.g. 30°13'28.9"N 30°49'1.5"E
	Degrees and decimal minutes, e.g. N30° 13.49760' , E30° 49.30788'
	Degrees minutes seconds, e.g. N30° 13' 29.8" , E30° 49' 1.5"
	Decimal degrees, e.g. 30.22496 , 30.821798

Southern hemisphere latitudes are given with a *S*, e.g. S30°, or with a
negative value, e.g. -30.22496. Similarly, western longitudes are given with a
*W*, e.g. W07°, or with a negative value, e.g. -7.34323.

*Divemaster*: The name of the dive master or dive guide for this dive should be
entered in this field
which offers auto completion based on the list of dive masters in
the current logbook.

*Buddy*: In this field, one enters the name(s) of the buddy / buddies
(separated with commas) who accompanied him/her on the
dive. Auto completion based on the list of buddies in the current logbook is
offered.

*Suit*: Here the type of diving suit used for the dive can be entered.
Auto completion of the suit description is available.

*Rating*: One can provide a subjective overall rating of the dive on a
5-point scale by clicking the appropriate star on the rating scale.

*Visibility*: Similarly, one can provide a rating of visibility during the
dive on a
5-point scale by clicking the appropriate star.

*Tags*: Tags that describe the type of dive performed can be entered
here (separated by commas). Examples of common tags are boat, drift, training,
cave, etc.
_Subsurface_ has many built-in tags. If the user starts typing a tag, the
program
will list the tags that correspond to the typing. For instance, if the user
typed
+cav+, then the tags *cave* and *cavern* are shown for the user to choose from.

*Notes*: Any additional information for the dive can be entered here.

The *Save* and *Cancel* buttons are used to save all the information for tabs
in the info panel and in the dive profile panel, so there's no need to use them
until ALL other information has been added. Here is an example of a completed
Dive Notes panel:

image::images/CompletedDiveInfo.jpg["FIGURE: A completed Dive Notes tab",align="center"]

==== Equipment

The Equipment tab allows one to enter information about the type of
cylinder and gas used as well as the weights used for the dive. The
message in a blue box at the top of the panel:

image::images/BlueEditBar.jpg["FIGURE: Blue edit bar",align="center"]

indicates that the dive is being edited.This is a highly interactive part of
_Subsurface_ and the information on
cylinders and gases (entered here) determines the behaviour of the dive profile
(top right-hand panel).

*Cylinders*: The cylinder information is entered through a dialogue that looks
like this:

image::images/CylinderDataEntry1.jpg["FIGURE: Initial cylinder dialogue",align="center"]

In most cases _Subsurface_ obtains the gas used from the dive computer and
automatically inserts the gas composition(% oxygen) in the table. The + button
at the top right allows the user to add more cylinders for this dive. The dark
dustbin icon on the left allows the deletion of information for a cylinder.

The user should start by selecting a cylinder type on the left-hand side of the
table.  To select a cylinder, the *cylinder type* box should be clicked. This
brings up a list button that can be used to display a dropdown list of
cylinders:

image::images/CylinderDataEntry2.jpg["FIGURE: The cylinder drop-down list button",align="center"]

The drop-down list can then be used to select the cylinder type that was used
for this dive or the user may start typing in the box which shows the available
options for the entered characters. The
*Size* of the cylinder as well as its working pressure (*WorkPress*) will
automatically be shown in the dialogue.

Next one must indicate the starting pressure and the ending pressure of the
specified gas during the dive. The unit of pressure (metric/imperial)
corresponds to the settings chosen in the _Preferences_.

Finally, the user must provide the gas mixture used. If air was used, the
value of 21%  can be entered  or this field can be left blank. If nitrox or
trimix were used, their percentages of oxygen and/or helium should be entered.
Any inappropriate fields should be left empty. After typing the
information for the cylinder,
either press _ENTER_ on the keyboard or click outside the cell
that contains
the cursor. Information for any additional cylinders can be added by using the +
button at the top right hand. Following is an example of a complete description
for a dive using two cylinders (air and EAN50):

image::images/CylinderDataEntry3.jpg["FIGURE: a completed cylinder dive information table",align="center"]

*Weights*: Information about the weight system used can be entered
using a dialogue very similar to that of the cylinder information. If one
clicks
the + button on the top right of the weights dialogue, the table looks like
this:

image::images/WeightsDataEntry1.jpg["FIGURE:The Weights dialogue",align="center"]

By clicking on the *Type* field, a drop-down list becomes accessible through a
down-arrow:

image::images/WeightsDataEntry2.jpg["FIGURE:Weights type drop-down list button",align="center"]

The drop-down list can then be used to select the type of weight system
used during the dive or the user may start typing in the box
which shows the available options for the entered characters.
In the *Weight*
field, type in the amount of weight used during the dive. After
specifying the weight
system, the user can either press _ENTER_ on the keyboard or click outside the
cell with the cursor.
It is possible to enter information for more than one weight system by adding
an additional system
using the + button on the top right hand. Weight systems can be deleted using
the dustbin icon on the left hand. Here is an example of information for a dive
with two types of weights: integrated as well as a weight belt:

image::images/WeightsDataEntry3.jpg["FIGURE: A completed weights information table",align="center"]

==== Saving the updated dive information

The information entered in the *Dive Notes* tab and the *Equipment* tab can be
saved by
using the
two buttons on the top right hand of the *Dive Notes* tab. If the _Save_ button
is clicked,
the dive data are saved. If the _Cancel_ button is clicked, then the newly
entered dive data are
deleted, although the dive profile obtained from the dive computer will be
retained. When the user exits _Subsurface_ there is a final prompt to confirm
that the new data should be saved.

=== Importing dive information from other digital data sources or other data formats

[[S_ImportingAlienDiveLogs]]

If a user has been diving for some time, it is possible that several dives were
logged using other dive log software. This information does not need retyping
because these divelogs can probably be
imported onto _Subsurface_. _Subsurface_ will import divelogs from a range of
other
dive log software. While some software is supported natively, for others the
user has to
export the logbook(s) to an intermediate format so that they can then be imported
by _Subsurface_.
Currently, _Subsurface_ supports importing CSV log files from several sources.
APD LogViewer, XP5 and Sensus files are
preconfigured, but because the import is flexible, users can configure their own
imports.
Manually kept log files (e.g. in spreadsheet) can also be imported by
configuring the CSV import.
_Subsurface_ can also import UDDF and UDCF files used by some divelog
software and some divecomputers, like the Heinrichs & Weikamp DR5. Finally,
for some divelog software like Mares Dive Organiser it is currently suggested to
import the logbooks first into a webservice like _divelogs.de_ and then import
them from there with
_Subsurface_, as divelogs.de supports a few additional logbook formats that
_Subsurface_ currently cannot parse.

When importing dives, _Subsurface_ tries to detect multiple records for
the same dive and merges the information as best as it can. If
there are no time zone issues (or other reasons that would cause the
beginning time of the dives to be significantly different) _Subsurface_
will not create duplicate entries.

==== Using the universal import dialogue
[[Unified_import]]

Importing dives from other software is performed through a universal interface
that is activated by selecting _Import_ from the Main Menu, then clicking on
_Import Log Files_. This brings up the dialogue *A* below.

image::images/Import1.jpg["FIGURE: Import dialogue: step 1",align="center"]

Towards the bottom right is a dropdown selector with a default label
of _Dive Log Files_ which gives access to the different types of direct imports
available, as in dialogue *B*, above. Currently these are:

 - XML-formatted dive logs (Divinglog 5.0, MacDive and several other dive log systems)
 - UDDF-formatted dive logs (e.g. Kenozoooid)
 - UDCF-formatted dive logs
 - JDiveLog
 - Suunto Dive Manager (DM3 and DM4)
 - CSV (text-based and spreadsheet-based) dive logs.

Selecting the appropriate file in the file list of the dialogue opens
the imported dive log in the _Subsurface_ *Dive List*. Some other formats, not
accessible through the Import dialogue are also supported, as explained below.

==== Importing from Mares Dive Organiser V2.1

Since Mares utilise proprietary Microsoft software not compatible with
multi-platform applications, these dive logs cannot be
directly imported into
_Subsurface_. Mares dive logs need to be imported using a three-step process,
using _www.divelogs.de_ as a mechanism to extract the dive log information.

1. The dive log data from Mares Dive Organiser need to be exported to the user's
desktop, using
 a _.sdf_ file name extension. Refer to xref:Mares_Export[Appendix C] for more
information.
2. Data should then be imported into _www.divelogs.de_. One needs to create a user
account in
_www.divelogs.de_, log into that web site, then
select _Import Logbook -> Dive Organiser_ from the menu on the left hand side.
The instructions must be carefully followed to transfer the dive information
(in _.sdf_ format) from the Dive Organiser data base to _www.divelogs.de_.
3. Finally,  import the dives
from _divelogs.de_ to _Subsurface_, using the instructions below.


[[S_ImportingDivelogsDe]]
==== Importing dives from *divelogs.de*

The import of dive information from _divelogs.de_ is simple, using a single
dialogue box. The _Import->Import form Divelogs.de_ option should be selected
from the Main Menu. This
brings up a dialogue box (see figure on left [*A*] below). Enter a
user-ID and password for _divelogs.de_ into the appropriate fields and then
select
the _Download_ button. Download from _divelogs.de_ starts immediately,
displaying a progress bar in the dialogue box. At the end of the download, the
success status is indicated (see figure on the right [*B*], below). The
_Apply_ button should then be selected, after which the imported dives appear in the
_Subsurface_ *Dive List* panel.

image::images/Divelogs1.jpg["FIGURE:Download from Divelogs.de",align="center"]


[[S_ImportingCSV]]
==== Importing dives in CSV format

Sometimes dive computers export dive information as files with
_comma-separated values_ (.CSV). For example, the APD Inspiration and Evolution
closed circuit rebreather (CCR) systems export dive information in a CSV
formatted file that normally contains information for a single dive only. These
files can easily be imported into _Subsurface_.
CSV files are normally organised into
a single line that provides the headers of the data columns, followed by the
data, one record per line. CSV files can be opened with a normal text editor.
Following is a highly simplified and shortened example of a CSV file from an
APD rebreather:

	Dive Time (s)	Depth (m)	PPO2 - Setpoint (Bar)	PPO2 - C1 Cell
1 (Bar)	Ambient temp. (Celsius)
	0	0.0	0.70	0.81	13.1
	0	1.2	0.70	0.71	13.1
	0	0.0	0.70	0.71	13.1
	0	1.2	0.70	0.71	13.2
	0	1.2	0.70	0.71	13.1
	10	1.6	0.70	0.72	12.7
	20	1.6	0.70	0.71	12.6
	30	1.7	0.70	0.71	12.6
	40	1.8	0.70	0.68	12.5
	50	1.6	0.70	0.68	12.5
	60	2.4	0.70	0.69	12.5
	70	3.5	0.70	0.69	12.4
	80	4.2	0.70	0.72	12.5
	90	4.0	0.70	0.71	12.4

Note that each title may comprise more than one word; for instance
'Dive Time (s)' in the above data example. Before being able to import the data
to _Subsurface_ one first needs to know:

a. Which character separates the different columns within a single line of
data? This field separator should be either a comma (,) or a TAB character.
This can be determined by opening the file with a text editor. If it is
comma-delimited, then the comma
characters between the values are clearly visible. If no commas are evident and
the numbers are aligned in columns,
the file is probably TAB-delimited (i.e. it uses a TAB as a field separator, as
in the above example).

b. Which data columns need to be imported into _Subsurface_? The Dive Time and
Depth columns are always required. Open the file using a text editor and note
the titles of the columns to be imported and their column positions. For
instance for the above example:

	Time:		column 1
	Depth:		column 2
	Temperature:	column 5
	ppO2:		column 4

Armed with this information, importing the data into _Subsurface_ is
straightforward. Select
_Import->Import Log Files_ from the main menu. In the resulting file
selection menu, select _CSV files_, after which a common configuration dialog
appears for all the
files with a CSV extension:

image::images/Import_CSV1.jpg["FIGURE: CSV download dialogue",align="center"]


There are pre-configured definitions for some dive computers, e.g. the APD
rebreathers. If the user's dive computer is on this list, it should be selected
using the dropdown
box labeled _Pre-configured imports_. Finally _OK_ should be clicked and
the dive will be imported and listed in the *Dive List* tab of _Subsurface_.

If the dive computer is not on the pre-configured list, the user must
select the _Field
Separator_ (TAB or comma) for the particular CSV file, using the appropriate
dropdown list. and indicate which columns in the CSV file
contain which data
variables. For each data column used for import, the user must check the
appropriate check box
and indicate in which column these data are found. For instance, the image above
corresponds to the dialogue that would apply to the CSV data set described above
the image. After completing the column specification, select the _OK_ button
and the dive will be imported and listed in the *Dive List* tab of _Subsurface_.


[[S_ImportingManualCSV]]
==== Importing dives from manually kept CSV file

If one keeps dive logs in a spreadsheet, there is an option to import
those dives as well. Spreadsheet data, exported as a CSV file, can
be imported to _Subsurface_. When importing manually
kept log files, the information needed is quite different as we are
importing only metadata, not profile samples.

Similarly to importing dives in CSV format (see above), one needs to
know the internal format
of the CSV data to import.

a. Which character separates the different columns within a single line of
data? This
should be either a comma (,), semicolon (;) or a TAB
character, and could be determined by opening the file with a text
editor. If it is comma-delimited, then the comma
characters between the values are clearly visible. If no commas are evident and
the data
are in clear columns, the file
is probably TAB-delimited (i.e. it uses a TAB as a field separator, as in the
above example).
A recommended field separator for the export is tab, as commas might be part of
the
field values themselves. Therefore the use of an appropriate field separator
in very important.

b. Which columns need to be imported into _Subsurface_? We do not
currently have any mandatory input fields, but some, e.g. dive duration
are crucial for the log file to make any sense. Possible options
can be seen in the image below and one should include all the
fields available in both your log file and in the _Subsurface_
import.

c. Units used for depth, weight and temperature. We consider depth to be
either feet or meters, weight kilograms or pounds and temperature either
Celsius or Fahrenheit. However, the users can select _Metric_ or
_Imperial_ in the _Preferences_ tab of _Subsurface_. No mixture of unit
systems is allowed for the different fields.

Importing manually kept CSV log files is quite straight forward, but
there might be many fields and counting the field numbers is error
prone. Therefore validation of the data to be imported is critical.

To import the dives, select _Import->Import Log Files_ from the menu
bar. If the CSV option in the dropdown list is selected and the file list
includes file names ending with .CSV, one can select the
_Manual dives_ tab that will bring up the following configuration dialog:

image::images/Import_CSV2.jpg["FIGURE: Download dialog for Manual CSV logs",align="center"]

The input fields can be configured as appropriate, and when everything is done
the _OK_ button should be selected to perform the import. New dives should
appear in the *Dive List* area of _Subsurface_.


[[S_Companion]]
=== Importing GPS coordinates with the _Subsurface Companion App_ for mobile phones

Using the *Subsurface Companion App* on an Android device with a GPS, the coordinates
for the diving
location can be automatically passed to the _Subsurface_
divelog. The Companion App stores the dive locations on
a dedicated Internet-based file server. _Subsurface_, in turn, can collect
the localities from the file server.

To do this:

==== Create a Companion App account

- Register on the http://api.hohndel.org/login/[_Subsurface companion web page_].
A confirmation email with instructions and a personal *DIVERID* will be sent,
a long number that gives access to the file server and Companion App capabilities.

- Download the app from
https://play.google.com/store/apps/details?id=org.subsurface[Google Play Store]
or from
http://f-droid.org/repository/browse/?fdfilter=subsurface&fdid=org.subsurface[F-Droid].

==== Using the Subsurface companion app on a smartphone

On first use the app has three options:

* _Create a new account._  Equivalent to registering in _Subsurface_ companion
page using an Internet browser. One can request a *DIVERID* using this option,
but this is supplied via email and followed up by interaction with the
http://api.hohndel.org/login/[_Subsurface companion web page_] in order to
activate the account.

* _Retrieve an account._  If users forgot their *DIVERID* they will receive an email
to recover the number.

* _Use an existing account._ Users are prompted for their *DIVERID*. The app saves
this *DIVERID* and does not ask for it again unless one uses the _Disconnect_ menu
option (see below).

[icon="images/icons/important.png"]
[IMPORTANT]
In the _Subsurface_ main program, the *DIVERID* should also be entered on the
Default Preferences
panel, obtained by selecting _File->Preferences->Defaults_ from the main menu
in _Subsurface_ itself.
This facilitates synchronisation between _Subsurface_ and the Companion App.

===== Creating new dive locations

Now one is ready to get a dive position and
send it to the server. The Android
display will look like the left hand image (*A*) below, but without any dive.

Touch the "+" icon on the top right to add a new dive site, a menu will be
showed with 3 options:

* Current: A prompt for a place name (or a request to activate the GPS if it is turned
off) will be displayed, after which the current location is saved.

* Use Map: This option allows the user to fix a position by searching a world map. A
world map is shown (see *B* below) on which one should indicate the desired position
with a _long press_ on the touch
sensitive screen (if the marked location is erroneous, simply indicate a new location)
and select the check symbol in the upper right. A dialog is shown allowing to enter the
name of the dive location and the date-time of the dive (see *C* below). In order to import this
dive location in _Subsurface_ it's advisable to set the time to agree with the time of
that dive on the dive computer.

image::images/Companion_5.jpg["FIGURE: Companion App, add location using map",align="center"]


* Import local GPX file: The android device searches for .gpx files and located
archives will be shown. The selected .gpx file is opened and the stored
locations shown. Now one needs to select the appropriate locations, then select the
tab in the upper right, after which the locations will be sent to the web service
and added to the list on the Android device.

===== Lists of dive locations

The main screen shows a list of dive locations, each with a name, date and
time (see *A* below). Some locations may have an arrow-up icon over the selection box to the left
indicating that they require upload to the server. One
can select individual dive locations from the list. A selected location has a
check mark in the selection box on the left. Group operations (such as _Delete_ or _Send_)
are performed on several locations that are selected.

Dive locations in this list can be viewed in two ways: a list of locations or a
map indicating the dive locations. The display mode (List or Map) is changed by
selecting _Dives_ at the top left of the screen (see *A* below) and then selecting
the display mode. The display mode can be changed either from the list
of locations or from the map (see *B* below). If one selects a location (on the list
or on the map), an editing
panel opens (see *C* below) where the dive description or other details may be changed.

image::images/Companion_4.jpg["FIGURE: Companion App, add location using map",align="center"]


When one clicks on a dive (*not* selecting the check box), the
name given to it, date/time and GPS coordinates will be shown, with two options at the top
of the screen:

- Edit (pencil):  Change the text name or other characteristics of the dive location.

- Maps:  Display a map showing the dive location.

After editing and saving a dive location (see *C* above), one needs to upload it to the web
service, as explained above.

===== Uploading dive locations

There are several ways to send locations to the server.
The easiest is by simply
selecting the locations (See *A* below) and then touching the right arrow at the
top right of the screen.

[icon="images/icons/important.png"]
[IMPORTANT]
Users must be careful, as the trash icon on the right means exactly what it should:
it deletes the selected dive location(s).

image::images/Companion_1.jpg["FIGURE: Screen shots (A-B) of companion app",align="center"]


After a dive trip using the Companion App, all dive locations are ready to be
downloaded to a _Subsurface_ dive log (see below).


===== Settings on the Companion app

Selecting the _Settings_ menu option results in the right hand image above (*B*).

===== Server and account

- _Web-service URL._ This is predefined (http://api.hohndel.org/)

- _User ID._ The DIVERID obtained by registering as described above. The easiest way to
obtain it is simply to copy and paste from the confirmation email but, of
course, users can also type this information.

===== Synchronization

- _Synchronize on startup._ If selected, dive locations in the Android device and those
on the web service synchronize each time the app is started.

- _Upload new dives._ If selected, each time the user adds a dive location it is
automatically sent to the server.

===== Background service
Instead of entering a unique dive location, users can leave the service running
in the background of their Android device, allowing the continuous collection of GPS locations.


The settings below define the behaviour of the service:

- _Min duration._ In minutes. The app will try to get a location every X minutes
until stopped by the user.

- _Min distance._ In meters. Minimum distance between two locations.

- _Name template._ The name the app will use when saving the locations.

[icon="images/icons/info.jpg"]
[TIP]
_How does the background service work?_ Assuming the user sets 5 minutes and 50
meters in the settings above, the app will start by recording a location at the current
location, followed by another one at every 5 minutes *or* every time one moves 50m
from previous location.
If subsequent locations are within a radius of 50 meters from the previous one,
a new location is not saved. If the user is not moving, only one location is saved,
but if the user is moving, a trace of the route is obtained by saving a
location every 50 meters.

===== Other

- _Mailing List._ The mail box for _Subsurface_. Users can send an email to the
Subsurface mailing list.

- _Subsurface website._ A link to the URL of Subsurface web

- _Version._ Displays the current version of the Companion App.

===== Search

Search the saved dive locations by name or by date and time.

===== Start service

Initiates the _background service_ following the previously defined settings.

===== Disconnect

This is a badly named option that disconnects the app from the server by
resetting the user ID in the app, showing the first screen where an account
can be created, retrieve the ID for an existing account or use the users own
ID. The disconnect option
is useful if a user's Android device was used to download the dive locations
of another registered diver.

===== Send all locations

This option sends all locations stored in the Android device to the server.


==== Downloading dive locations to the _Subsurface_ divelog

Download dive(s) from a dive computer or enter them manually into
_Subsurface_ before obtaining the GPS coordinates from the server. The download
dialog can be reached via _Ctrl+G_ or from the _Subsurface_ Main Menu _Import
-> Import GPS data from Subsurface Service_, resulting in the image on the
left (*A*), below. On first use the DIVERID text box is blank. Provide a
DIVERID, then select the _Download_ button to initiate the download process, after
which the screen on the right (*B*) below appears:

image::images/DownloadGPS.jpg["FIGURE: Downloading Companion app GPS data",align="center"]

Note that the _Apply_ button is now active. By clicking on it, users can update the locations
of the newly entered or uploaded dives in _Subsurface_ which applies the
coordinates and names entered on the app for all the new dives that match the
date-times of the uploaded GPS localities. If one has entered the name of the dive
location in _Subsurface_ before downloading the GPS coordinates, this name will take
precedence over downloaded one.

Since _Subsurface_ matches GPS locations from the Android device and dive information from the
dive computer based on date-time data, automatic assignment of GPS data to dives is dependent
on agreement of the date-time information between these two devices. Although _Subsurface_ has
a wide range tolerance, it may be unable to identify the appropriate dive if there is
a large difference between the time in the dive computer and that of the Android device,
resulting in no updates.

Similar date-times may not always be possible and there may be many reasons for this (e.g. time zones), or
_Subsurface_ may be unable to decide which is the correct position for a dive (e.g. on repetitive
dives while running _background service_ there may be several locations that would be
included in the time range that fit not only the first dive, but one or more subsequent dives as well).
A workaround for this situation to manually edit the date-time of a dive in the _Subsurface_
Dive List *before* downloading the GPS data and then to change the date-time back again *after*
downloading GPS data.

[icon="images/icons/info.jpg"]
[NOTE]
TIPS:

- _Background service_, being a very powerful tool, may fill the location list with
many unnecessary locations not corresponding to the exact dive point but reflecting the boat's route.
Currently these locations are difficult to delete from the server. In some situations it
is therefore prudent to clean up the list on the Android device before sending the dive points to the web
server by simply deleting the inappropriate locations. This might be necessary, for
instance, if one wants to keep the location list clear to see dives in the web service map display (see above).

- It may also make sense to give informative names to the locations sent to the web server, or at least
to use an informative name in the _Name Template_ setting while running the _background service_,
especially on a dive trip with many dives and dive locations.

== Obtaining more information about dives entered into the logbook

=== The *Dive Info* tab (for individual dives)

The Dive Info tab gives some summary information about a particular dive that
has been selected in the *Dive List*. Useful information here includes the
surface interval before the dive, the maximum and mean depths of the dive, the
gas volume consumed, the surface air consumption (SAC) and the number of oxygen
toxicity units (OTU) incurred.

[icon="images/icons/info.jpg"]
[NOTE]
Gas consumption and SAC calculations:
_Subsurface_ calculates SAC and Gas consumption taking in account gas
incompressibility, particularly at tank pressures above 200 bar, making them more accurate.
Users should refer to xref:SAC_CALCULATION[Appendix D] for more information.

=== The *Stats* tab (for groups of dives)

The Stats tab gives summary statistics for more than one dive, assuming that
more than one dive have been selected in the *Dive List* using the standard
Ctrl-click or Shift-click of the mouse. If only one
dive has been selected, figures pertaining to only that dive are given. This tab
shows the number of dives selected, the total amount of dive time in these
dives,
as well as the minimum, maximum and mean for the dive duration, dive depth,
water temperature and surface air consumption (SAC).

[[S_DiveProfile]]
=== The *Dive Profile*

image::images/Profile2.jpg["Typical dive profile",align="center"]

Of all the panels in _Subsurface_, the Dive Profile contains the most detailed
information about each dive. The Dive Profile has a *button bar* on the left hand side
that allows control over several display options. The functions of these
buttons are described below. The main item in the Dive
Profile is the graph of
dive depth as a function of time. In addition to the obvious information of
the depth it also shows the ascent and descent rates compared to the recommended
speed of going up or down in the water column. This information is given using
different colours:
|====================
|*Colour*|*Descent speed (m/min)*|*Ascent speed (m/min)*
|Red|> 30|> 18
|Orange|18 - 30|9 - 18
|Yellow|9 - 18|4 - 9
|Light green|1.5 - 9|1.5 - 4
|Dark green|< 1.5|< 1.5
|=====================

The profile also includes depth readings for the peaks and troughs in the graph.
Thus, users should see the depth of the deepest point and other peaks. Mean depth
is marked with a horizontal red line.

[icon="images/icons/scale.jpg"]
[NOTE]
In some cases the dive profile does not fill the whole area of the *Dive Profile*
panel. Clicking the *Scale* button in the toolbar on the left of the dive profile
frequently increases the size of the dive profile to fill the area of the panel efficiently.

*Water temperature* is displayed with its own blue line with temperature values
placed adjacent to significant changes.

The dive profile can include graphs of the *partial pressures*
of O2, N2, and He during the dive (see figure above) as well as a calculated and dive computer
reported deco ceilings (only visible for deep, long, or repetitive dives). Partial pressures of oxygen are indicated in green, those of nitrogen in black, and those of helium in dark red. These
partial pressure graphs are shown below the profile data.

[icon="images/icons/O2.jpg"]
[NOTE]
Clicking this button allows display of the partial pressure of *oxygen* during the
dive. This is depicted below the dive depth and water temperature graphs.

[icon="images/icons/N2.jpg"]
[NOTE]
Clicking this button allows display of the partial pressure of *nitrogen* during the dive.

[icon="images/icons/He.jpg"]
[NOTE]
Clicking this button allows display of the partial pressure of *helium* during the dive.
This is only of importance to divers using Trimix, Helitrox or similar breathing gasses.

The *air consumption* graph displays the tank pressure and its change during the
dive. The air consumption takes depth into account so that even when manually
entering the start and end pressures the graph is not a straight line.
Similarly to the depth graph the slope of the tank pressure gives the user information
about the
momentary SAC rate (Surface Air Consumption) when using an air integrated dive computer.
Here the colour
coding is not relative to some absolute values but relative to the average
normalised air consumption during the dive. So areas that are red or orange
indicate
times of increased normalized air consumption while dark green reflects times
when the diver was using less gas than average.

[icon="images/icons/Heartbutton.png"]
[NOTE]
Clicking on the heartrate button will allow the display of heart rate information
during the dive if the dive computer was attached to a heart rate sensor.

It is possible to *zoom* into the profile graph. This is done either by using
the scroll wheel / scroll gesture of your mouse or trackpad. By default
_Subsurface_ always shows a profile area large enough for at least 30 minutes
and 30m
 (100ft) – this way short or shallow dives are intuitively recognizable;
something
that free divers clearly won’t care about.

image::images/MeasuringBar.png["FIGURE: Measuring Bar",align="center"]

[icon="images/icons/ruler.jpg"]
[NOTE]
Measurements of *depth or time differences* can be achieved by using the
*ruler button* on the left of the dive profile panel.
The measurement is done by dragging the red dots to the two points
on the dive profile that the user wishes to measure. Information is then given
in the horizontal white area underneath the
two red dots.

The profile can also include the dive computer reported *ceiling* (more
precisely, the deepest deco stop that the dive computer calculated for each
particular moment in time) as a red overlay on  the dive profile. Ascent ceilings
arise when a direct ascent to the surface increases
the risk of a diver suffering from decompression sickness (DCS) and it is necessary
to either ascend
slower or to perform decompression stop(s) before ascending to the surface. Not
all dive computers record this information and make it available for download;
for example all of the Suunto dive computers fail to make this very useful data
available to divelog software. _Subsurface_ also calculates ceilings independently,
shown as a green overlay on the dive profile.
Because of the differences in algorithms used
and amount of data available (and other factors taken into consideration at the time
of the calculation) it is unlikely that ceilings from dive computers and from _Subsurface_
are the same, even if the same algorithm and _gradient factors_ (see below) are used.
It is also quite common that _Subsurface_ calculates a ceiling for
non-decompression dives when the dive computer stayed in non-deco mode during
the whole dive (represented by the [green]#dark green# section in the profile
at the beginning of this section). This is caused by the fact that
_Subsurface’s_
calculations describe the deco obligation at each moment during a dive,
while dive computers usually take the upcoming ascent into account. During the
ascent some excess nitrogen (and possibly helium) are already breathed off so
even
though the diver technically encountered a ceiling at depth, the dive still does
not require an explicit deco stop. This feature allows dive computers to offer
longer non-stop bottom times.

[icon="images/icons/cceiling.jpg"]
[NOTE]
If the dive computer itself calculates a ceiling and makes it available to
_Subsurface_ during upload of dives, this can be
shown as a red area by checking *Dive computer reported ceiling* button on the Profile Panel.

[icon="images/icons/ceiling1.jpg"]
[NOTE]
If the *Calculated ceiling* button on the Profile Panel is clicked, then a ceiling,
calculated by _Subsurface_, is shown in green if it exists for
a particular dive (*A* in figure below). This setting can be modified in two ways:

[icon="images/icons/ceiling2.jpg"]
[NOTE]
If, in addition, the *show all tissues* button on the Profile Panel is clicked, the ceiling is shown for the tissue
compartments following the Bühlmann model (*B* in figure below).

[icon="images/icons/ceiling3.jpg"]
[NOTE]
If, in addition, the *3m increments* button on the Profile Panel is clicked, then the ceiling is indicated in 3 m increments
(*C* in figure below).

image::images/Ceilings2.jpg["Figure: Ceiling with 3m resolution",align="center"]

Gradient Factor settings strongly affect the calculated ceilings and their depths.
For more information about Gradient factors, see the section on xref:S_GradientFactors[Gradient Factor Preference settings]. The
currently used gradient factors (e.g. GF 35/75) are shown above the depth profile if the appropriate toolbar buttons are activated.
*N.B.:* The indicated gradient factors are NOT the gradient factors in use by the dive computer,
but those used by _Subsurface_ to calculate deco obligations
during the dive. For more information external to this manual see:

 ** http://www.tek-dive.com/portal/upload/M-Values.pdf[Understanding M-values by Erik Baker, _Immersed_ Vol. 3, No. 3.]

 ** link:http://www.rebreatherworld.com/general-and-new-to-rebreather-articles/5037-gradient-factors-for-dummies.html[Gradient factors for dummies, by Kevin Watts]


=== The Dive Profile context menu

The context menu for the Dive Profile is accessed by right-clicking while the
mouse cursor is over the Dive Profile panel. The menu allows the creation of
Bookmarks or Gas Change Event markers other than the ones that might have been
imported from a Dive Computer. Markers are placed against the depth profile line
and with the time of the event set by where the mouse cursor was when the right
mouse button was initially clicked to bring up the menu. Gas Change events
open a further selection of which gas is being switched to, the list based on
the available gases defined in the Equipment Tab. By right-clicking while over
an existing marker, the menu extends adding options to allow deletion of the
marker or to allow all markers of that type to be hidden. Hidden events can be
restored to view by selecting Unhide all events from the context menu.

=== The *Information Box*

The Information box displays a large range of information pertaining to the dive
profile. Normally the Information Box is located to the top left of the *Dive
Profile* panel. If the mouse points outside of the *Dive Profile* panel, then
only the top line of the Information Box is visible (see left-hand part of
figure (*A*) below). The Information Box can be moved around in the *Dive Profile*
panel by click-dragging it with the mouse so that it is not obstructing
important detail. The position of the Information Box is saved and used again
during subsequent dive analyses.

image::images/InfoBox2.jpg["Figure: Information Box",align="center"]

The moment the mouse points inside the *Dive Profile* panel, the information box  expands and
shows many data items. In this situation, the data reflect the time point along
the dive profile indicated by the mouse cursor (see right-hand part of figure (*B*) above
where the Information Box reflects the situation at the position of the cursor
[arrow] in that image). Therefore, moving the cursor in the horizontal
direction allows the Information Box to show information for any point along the
dive profile.
In this mode, the Information Box gives extensive statistics about depth, gas
and ceiling characteristics of the particular dive. These include: Time period
into the dive (indicated by a @), depth, cylinder pressure (P), temperature,
ascent/descent rate, surface air consumption (SAC), oxygen partial pressure,
maximum operating depth, equivalent air depth (EAD), equivalent narcotic depth
(END), equivalent air density depth (EADD), decompression requirements at that
instant in time (Deco), time to surface (TTS), the calculated ceiling, as well
as the calculated ceiling for several Bühlmann tissue compartments.

The user has control over the display of several statistics, represented as four
buttons on the left of the profile panel. These are:

[icon="images/icons/MOD.jpg"]
[NOTE]
Clicking this button causes the Information Box to display the *Maximum Operating Depth
(MOD)* of the dive, given the
gas mixture used. MOD is dependent on the oxygen concentration in the breathing gas.
For air (21% oxygen) it is around 57 m. Below the MOD there is a markedly increased
risk of exposure to the dangers associated with oxygen toxicity.

[icon="images/icons/NDL.jpg"]
[NOTE]
Clicking this button causes the Information Box to display the *No-deco Limit (NDL)* or the
*Total Time to Surface (TTS)*. NDL is the time duration that a diver can continue with a
dive, given the present depth, that does not require decompression (that is, before an
ascent ceiling appears). Once one has exceeded the NDL and decompression is required (that
is, there is an ascent ceiling above the diver, then TTS gives the number of minutes
required before the diver can surface. TTS includes ascent time as well as decompression
time.

[icon="images/icons/SAC.jpg"]
[NOTE]
Clicking this button causes the Information Box to display the *Surface Air Consumption (SAC)*.
SAC is an indication of the surface-normalised respiration rate of a diver. The value of SAC
is less than the real
respiration rate because a diver at 10m uses breathing gas at a rate roughly double that of
the equivalent rate at the surface. SAC gives an indication of breathing gas consumption rate
independent of the depth of the dive so that the respiratory rates of different dives
can be compared. The units for SAC is litres/min or cub ft/min.

[icon="images/icons/EAD.jpg"]
[NOTE]
Clicking this button displays the *Equivalent Air Depth (EAD)* for
nitrox dives as well as the *Equivalent
Narcotic Depth (END)* for trimix dives. These are numbers of
importance to divers who use breathing gases other than air. Their
values are dependent on the composition of the breathing gas.  The EAD
is the depth of a hypothetical air dive that has the same partial
pressure of nitrogen as the current depth of the nitrox dive at
hand. A nitrox dive leads to the same decompression obligation as an
air dive to the depth equalling the EAD. The END is the depth of a
hypothetical air dive that has the same sum of partial pressures of
the narcotic gases nitrogen and oxygen as the current trimix dive. A
trimix diver can expect the same narcotic effect as a diver breathing
air diving at a depth equalling the END.

Figure (*B*) above shows an information box with a nearly complete set of data.

== Organising the logbook (Manipulating groups of dives)

=== The Dive List context menu

Many actions within _Subsurface_ are dependent on a context menu used
mostly to manipulate  groups of dives. The context menu is found by selecting
a dive or a group of dives and then right-clicking.

image::images/ContextMenu.jpg["Figure: Context Menu",align="center"]

The context menu is used in many manipulations described below.

[[S_Renumber]]
=== Renumbering the dives

Dives are normally numbered incrementally from non-recent dives (low sequence
numbers) to recent dives (having the highest sequence numbers). The numbering
of the dives is not always consistent. For instance, when non-recent dives are
added to the dive list the numbering does not automatically follow on because
of the dives that are more recent in date/time than the newly-added dive with
an older date/time. Therefore, one may sometimes need to renumber the dives.
This is performed by selecting (from the Main Menu) _Log -> Renumber_. Users are
given a choice with respect to the lowest sequence number to be used.
Completing this operation results in new sequence numbers (based on date/time)
for the dives in the *Dive List* panel.

[[S_Group]]
=== Grouping dives into trips and manipulating trips

For regular divers, the dive list can rapidly become very long. _Subsurface_
can group dives into _trips_. It performs this by grouping dives that have
date/times that are not separated in time by more than two days, thus creating
a single heading for each diving trip represented in the dive log. Below is an
ungrouped dive list (*A*, on the left) as well as the corresponding grouped dive
list comprising five dive trips (*B*, on the right):

image::images/Group2.jpg["Figure: Grouping dives",align="center"]

Grouping into trips allows a rapid way of accessing individual dives without
having to scan a long lists of dives. In order to group the dives in a dive list,
(from the Main Menu) users must select _Log -> Autogroup_. The *Dive List* panel
now shows only the titles for the trips.

==== Editing the title and associated information for a particular trip

Normally, in the dive list, minimal information is included in the trip title.
More information about a trip can be added by selecting its trip title from
the *Dive list*. This shows a *Trip Notes* tab in the *Dive Notes* panel. Here
users can add or edit information about the date/time, the trip location and any
other general comments about the trip as a whole (e.g. the dive company that was
dived with, the general weather and surface conditions during the trip, etc.).
After entering this
information, users should select *Save* from the buttons at the top right
of the *Trip Notes*
tab. The trip title in the *Dive List* panel should now reflect some of the
edited information.

==== Viewing the dives during a particular trip

Once when the dives have been grouped into trips, users can expand one or more
trips by clicking the arrow-head on the left of each trip title. This expands
the selected trip, revealing the individual dives performed during the trip.

==== Collapsing or expanding dive information for different trips

If a user right-clicks after selecting a particular trip in the dive list, the
resulting context menu allows several possibilities to expand or collapse dives
within trips. This includes expanding all trips, collapsing all trips and
collapsing all trips except the selected one.

==== Merging dives from more than one trip into a single trip

By right-clicking on a selected trip title in the *Dive List* panel, a
context menu shows up that allows the merging of trips by either merging of the selected trip
with the trip below or with the trip above.

==== Splitting a single trip into more than one trip

If a trip includes five dives, the user can split this trip into two trips (trip 1:
top 3 dives; trip 2: bottom 2 dives) by selecting and right-clicking the top
three dives. The resulting context menu allows the user to create a new trip by
choosing the option *Create new trip above*. The top three dives are then
grouped
into a separate trip. The figures bellow shows the selection and context menu
on the left (A) and
the completed action on the right (B):

image::images/SplitDive3a.jpg["FIGURE: Split a trip into 2 trips",align="center"]

=== Manipulating single dives

==== Delete a dive from the dive log

Dives can be permanently deleted from the dive log by selecting and
right-clicking them to bring up the context menu, and then selecting *Delete
dive(s)*. Typically this would apply to a case where a user wishes to delete
workshop
calibration dives of the dive computer or dives of extremely short duration.

==== Unlink a dive from a trip

Users can unlink dives from the trip to which they belong. In order to do this,
select and right-click
the relevant dives to bring up the context menu. Then select the option *Remove dive(s)
from trip*. The dive(s) now appear immediately above the trip to
which they belonged.

==== Add a dive to the trip immediately above

Selected dives can be moved from the trip to which they belong and placed within
the trip immediately above the currently active trip. To do this, select
and right-click
the dive(s) to bring up the context menu, and then select *Add dive(s) to trip
immediately above*.

==== Shift the start time of dive(s)

Sometimes it is necessary to adjust the start time of a dive. This may apply to
situations where dives are performed in different time zones or when the dive
computer has an erroneous time. In order to do this, user must select and right-click
the dive(s) to be
adjusted. This action brings up the context menu on which the *Shift times*
option should be selected. User must then specify the
time
(in hours and minutes) by which the dives should be adjusted and click on the
option indicating whether the time adjustment should be forwards or backwards.

==== Merge dives into a single dive

Sometimes a dive is briefly interrupted, e.g. if a diver returns to the surface
for a few minutes, resulting in two or more dives being recorded by the dive
computer and appearing as different dives in the *Dive List* panel. Users can
merge these dives onto a single dive by selecting the appropriate dives,
right-clicking them to bring up the context menu and then selecting *Merge selected
dives*. It may be necessary to edit the dive information in the *Dive Notes*
panel to reflect events or conditions that apply to the merged dive. The figure
below shows the depth profile two such dives that were merged:

image::images/MergedDive.png["Example: Merged dive",align="center"]

[[S_ExportLog]]
== Exporting the dive log or parts of the dive log

A dive log can be saved in three formats:

* _Subsurface_ XML format. This is the native format used by _Subsurface_.

* Universal Dive Data format (UDDF). Refer to http://uddf.org for more information.
UDDF is a generic format that enables communication among many dive computers
and computer programs.

* CSV format, that includes the most critical information of the dive
profile. Included information of a dive is: number, date, time,
duration, depth, temperature and pressure.

In order to save the WHOLE dive log (i.e. all trips and dives), select *File*
from the Main menu. To save in _Subsurface_ XML format, select _File -> Save as_.
To save in UDDF format, select _File -> Export UDDF_ and to save in CSV
format, select _File -> Export CSV_.

In order to save only one or more dives or one or two trips, select the
appropriate dives or trips in the *Dive List* panel and then right-click the
selected dives to bring up the context menu. To save in _Subsurface_ XML
format, select _Save as_ from the context menu. To save in UDDF or CSV
format, select _Export as UDDF_ or _Export as CSV_ from the context menu
respectively.

Export to other formats can be achieved through third party facilities, for
instance _www.divelogs.de_.

[[S_PrintDivelog]]
== Printing a dive log

_Subsurface_ provides a simple interface to print a whole dive log or only a
few selected dives, including dive profiles and other contextual information.

Before printing, two decisions are required:

- Should the whole dive log be printed or only part of it? If only part of the
dive log is required, then the user must select the required dives from the *Dive List* panel.
- What gas partial pressure information is required on the dive profile? Users should select
the appropriate information from the Main Menu: _File->Preferences->Graph_.

Now the print options should be selected to match the user's needs. To do this, user should select _File->Print_ from
the Main menu. The following dialogue appears (see the image on the left [A],
below).

Under _Print type_ users need to select one of three options:

- Print the Dive List: to do this, _Table Print_ should be selected.
- Print the full dive records (dive profiles and all other information) at 6
dives per printed page: to do this, users should select _6 dives per page_.
- Print the full dive records (dive profiles and all other information) at 2
dives per printed page: to do this, users should select _2 dives per page_.

Under _Print options_ users need to select:

- Printing only the dives that have been selected from the dive list prior to
activating the print dialogue, achieved by checking the box _Print only
selected dives_.
- Printing in colour, achieved by checking the box with _Print in color_.

The _Ordering_ affects the layout of the page (or part of it) for each dive.
The dive profile could be printed at the top of each dive, with the textual
information underneath, or it could be printed with the textual information at
the top with the dive profile underneath. Users should select the appropriate option in the
print dialogue. See the image on the right (*B*), above which has a layout with
text above the dive profile.

Users can _Preview_ the printed page by selecting the _Preview_ button on the
dialogue. After preview, changes to the options in the print dialogue can be
made, resulting in a layout that fits personal taste.

image::images/PrintDiveLog.jpg["FIGURE: Print dialogue",align="center"]

Next, select the _Print_ button in the dialogue. This activates the regular print
dialogue used by the user operating system (image [*B*] in the middle, above),
allowing them to choose a printer and to set its properties (image [*C*] on the right,
above).
It is important to set the print resolution of the printer to an appropriate value by
changing
the printer properties. Finally, users can print their dives. Below is a (rather small)
example of
the output for one particular page.

image::images/Printpreview.jpg["FIGURE: Print preview page",align="center"]


[[S_Preferences]]
== Setting user _Preferences_ for _Subsurface_

There are several settings within _Subsurface_ that the users can specify. These
are found when selecting _File->Preferences_. The settings are performed in
four groups: *Defaults*, *Units*, *Graph* and *Language*. All four sections
operate on the same principles: the user must specify the settings the are to be changed, then
these changes are saved using the *Apply* button. After applying all the new settings users can then
leave the settings panel by selecting *OK*.

=== Defaults

There are four settings in the *Defaults* panel:

image::images/Preferences1.jpg["FIGURE: Preferences defaults page",align="center"]

  ** *Lists and tables*: Here one can specify the font type and font size of the
Dive Table panel. By decreasing the font size of the Dive table, users can see more dives on a screen.

  ** *Dives*: For the _Default Dive File_ one need to specify the directory and
file name of one's
electronic dive log book. This is a file with filename extension .xml. When
launched, _Subsurface_ will then automatically load the specified dive log book.

  ** *Display invalid*:  Dives can be marked as invalid (when a user wishes to hide
dives that he/she don't consider valid dives, e.g. pool dives, but still want to
keep them in the dive log). This controls whether those dives are displayed in
the dive list.

  ** *Use Default cylinder*: Here users can specify the default cylinder listed in
the *Equipment* tab of the *Dive Notes* panel.

  ** *Animations*: Some actions in showing the dive profile are performed using
animations. For instance, the axis values for depth and time change from dive to
dive. When viewing a different dive, these changes in axis characteristics do not
happen instantaneously, but are animated. The _Speed_ of animations can be controlled
by setting this slider
with faster animation speed to the left, with a 0 value representing no animation
at all.

=== Units
image::images/Preferences2.jpg["FIGURE: Preferences Units page",align="center"]

Here user can choose between metric and imperial units of depth, pressure,
volume, temperature and mass. By selecting the Metric or Imperial radio button
at the top, users can specify that all units are in the chosen measurement system.
Alternatively, if one selects the *Personalise* radio button, units can be selected
independently, with some units in the metric system and other in the imperial.

=== Graph
image::images/Preferences3.jpg["FIGURE: Preferences Graph page",align="center"]

[[S_GradientFactors]]
This panel allows two type of selections:

* *Show*: Here users can specify the amount of information shown as part of
the dive profile:
** Gas pressure graphs: _Subsurface_ can display the nitrogen, oxygen and the helium partial pressures during
the dive. These are enabled using the toolbar on the left hand side of the *Dive Profile*
panel. For each of these graphs users can specify a threshold value on the right-hand side of the
Preferences panel. If any of the graphs go above this threshold level, the graph is
highlighted in red, indicating that the threshold has been exceeded.

** _draw dive computer reported ceiling red_: This checkbox allows exactly what it says.
Not all dive computers report ceiling values. If the dive computer does report it, it may differ
from the ceilings calculated by Subsurface. This is because of the different algorithms and gradient factors available for calculating ceilings, as well as the dynamic way that a
dive computer can calculate ceilings during a dive.

** _Show non-used cylinders in Equipment Tab_: This checkbox allows display of information about non-used cylinders when viewing the *Equipment Tab*. Conversely, if this box is un-checked, and any cylinders entered using the *Equipment Tab* are not used (e.g. there was no gas switch to such a cylinder), then these cylinders are omitted from that list.

** _show average depth_: Activating this checkbox causes Subsurface to draw a red line across
the dive profile, indicating the mean depth of the dive.

* *Misc*: *Gradient Factors:* Here users can set the _gradient factors_ used while diving. GF_Low is
the gradient factor at depth and GF_High is used just below the surface.
At intermediate depths gradient factors between GF_Low and GF_High are used.
Gradient factors add conservatism to the nitrogen exposure during a dive, in a
similar way that many dive computers have a conservatism setting. The lower
the value of a gradient factor, the more conservative the calculations are with
respect to nitrogen loading and the deeper the ascent ceilings are. Gradient
factors of 20/60 are considered conservative and values of 60/90 are considered
harsh. Checking *GFLow at max depth* box causes GF_Low to be used at the
deepest depth of a dive. For more information see:

 ** http://www.tek-dive.com/portal/upload/M-Values.pdf[Understanding M-values by Erik Baker, _Immersed_ Vol. 3, No. 3.]

 ** link:http://www.rebreatherworld.com/general-and-new-to-rebreather-articles/5037-gradient-factors-for-dummies.html[Gradient factors for dummies, by Kevin Watts]

=== Languages
A checkbox allows one to use the _System Default_ language which in most cases
will be the correct setting; with this _Subsurface_ simply runs in the same
language / country settings as the underlying OS. If this is for some reason
undesirable users can uncheck this checkbox and pick a language / country
combination from the list of included localizations.

[[S_DivePlanner]]
== The Subsurface dive planner
The dive planner is accessed by selecting _Log -> Plan Dive_ from the main menu. This
feature IS EXPERIMENTAL and assumes the user is already familiar with the _Subsurface_
user interface. It is explicitly used under the following conditions:

- The user is conversant with dive planning and has the necessary training to perform
dive planning.
- The user plans dives within his/her certification limits.
- Dive planning makes large assumptions about the characteristics of the _average person_
and cannot compensate for individual physiology or health or personal history or
life style characteristics.
- The safety of a dive plan depends heavily on the way in which the planner is used.
- A user who is not absolutely sure about any of the above requirements should not use
this feature.

The dive planner currently comprises two parts: constructing a dive plan and evaluating
that dive plan. Currently the only evaluation available is with respect to dive
ceilings and maximal partial gas pressures. To perform dive planning, perform these steps:

- Clear the existing dive log by creating a new planning log. This achieved by selecting
_File -> New logbook_ from the main menu. This way, dive plans are kept totally separate
from the existing dive log of completed dives.

- In the top right-hand area of the screen, ensure that the constant dive parameters are
appropriate. These are: ATM Pressure, Bottom SAC, SAC on Deco, GFHigh, GFLow and whether
the last deco stop should be at 6m instead of the default 3m.

- In the table labeled _Available Gases_, add the information of the cylinders to be used
as well as the gas composition within that cylinder. This is done in a similar way as for
<<S_CylinderData,providing cylinder data for dive logs>>.

- Construct a dive profile, using similar procedures as for <<S_CreateProfile,hand-creating a dive profile>>
in the sections above. The unique feature of _Subsurface_ is the graphical interface
for constructing dive plans. Drag the profile around using the waypoints on the
design screen on the right, create more waypoints by double-clicking on the profile
line and ensuring that the profile reflects the intended dive.

- Indicate any changes in gas cylinder used by indicating gas changes as explained
in the section <<S_CreateProfile,hand-creating a dive profile>>. These changes should
reflect the cylinders and gas compositions defined in the table with _Available Gases_.

- Each waypoint on the dive profile creates a _Dive Planner Point_ in the table on the
bottom left of the dive planner panel. Ensure that the _Used Gas_ value in each row
of that table corresponds to one of the gas mixtures specified in the table with
_Available Gases_ immediately above the Dive Planner Points.

- Add new waypoints until the main features of the dive have been completed, e.g. the
bottom time segment and deep stops (if these are implemented). Leave the remaining
waypoints on the ascent to _Subsurface_. In most cases _Subsurface_
computes additional way points in order to fulfill decompression requirements for that
dive. These appear in the table with _Computed Waypoints_ to the right of the Dive Planner
Points.

Below is an example of a dive plan to 40m using EAN28:

image::images/Planner1.jpg["FIGURE: Planning a dive: setup",align="center"]

Once the above has been completed, one can save it by clicking the _Save_ button
towards the middle bottom of the dive planner panel. The saved dive plan will appear
in the *Dive List* panel.

The dive plan can be evaluated by doing the following:

- Ensure that the appropriate gradient factors have been selected in the _Preferences_
panel of _Subsurface_.

- Ensure that the appropriate maximal partial pressures of the gases used have been
specified in the _Preferences_ panel of _Subsurface_.

- Select the appropriate dive plan from the *Dive List* panel.

- Ensure that the appropriate button(s) for the display of the calculated ceiling have
been activated on the left part of the *Dive Profile* panel.

- Ensure that the appropriate button(s) for the display of the partial pressures of gases
(PO2, PN2, PHe) have been activated on the left part of the *Dive Profile* panel.

The dive profile is shown in conjunction with the relevant dive ceiling. The dive profile
should not closely approach the calculated ceiling. The partial gas pressures selected for
display are indicates as graphs below the dive profile. The partial pressures of any of the
gasses should not exceed the limits defined in the _Preferences_ panel of _Subsurface_. If
any of the gases exceed the specified partial pressures, the appropriate segments of the
dive profile is highlighted in red.

Below is the dive plan completed in the previous figure which can now be evaluated
against the ceiling (determined by the gradient factors) as well as against the
maximum gas partial pressures. Notice the plan is deficient in terms of gas planning:
there is no provision for any reserve gas.

image::images/Planner2.jpg["FIGURE: Planning a dive: evaluation",align="center"]

This part of the software is in active development.

== Description of the Subsurface Main Menu items

This section describes the functions and operation of the items in the Main Menu
of Subsurface. Several of the items below are links to sections of this manual
dealing with the appropriate operations.

=== File
- <<S_NewLogbook,_New Logbook_>> - Close the currently open dive logbook and
clear all dive information.
- _Open logbook_ - This opens the file manager in order to select a dive
logbook to open.
- _Save_ - Save the dive logbook that is currently open.
- _Save as_: - Save the current logbook or the currently selected dives within
the present logbook under a different filename.
- _Close_ -  Close the dive logbook that is currently open.
- <<S_ExportLog,_Export UDDF_>> -  Export the currently open dive logbook (or
the selected dives in the logbook) in UDDF format.
- _Export HTML World Map_ - Export the currently open dive logbook locations
in HTML format and draw these on a world map. The dive notes and some other information
about each dive can be viewed by hovering over each dive location.
- <<S_PrintDivelog,_Print_>> -  Print the currently open logbook.
- <<S_Preferences,_Preferences_>> -  Set the _Subsurface_ preferences.
- _Quit_ - Quit _Subsurface_.

=== Import
- <<S_ImportDiveComputer,_Import from dive computer_>> - Import dive information
from a dive computer.
- <<Unified_import,_Import Log Files_>> - Import dive information from a file in
in a _Subsurface_-compatible format.
- <<S_Companion,_Import GPS data from Subsurface Service_>> - Load GPS
coordinates from the _Subsurface_ mobile phone app.
- <<S_ImportingDivelogsDe,_Import from Divelogs.de_>> - Import dive information
from _www.Divelogs.de_.

=== Log
- <<S_EnterData,_Add Dive_>> - Manually add a new dive to the *Dive List* panel.
- <<S_Renumber,_Renumber_>> - Renumber the dives listed in the *Dive List*
panel.
-_Plan Dive_ - This experimental feature allows planning of simple dives.
- <<S_Group,_Auto Group_>> - Group the dives in the *Dive List* panel into dive
trips.
- _Edit Device Names_ - Edit the names of dive computers.

=== View
- <<S_ViewPanels,_All_>> - View the four main _Subsurface_ panels
simmultaneously.
- <<S_ViewPanels,_Dive List_>> - View only the *Dive List* panel.
- <<S_ViewPanels,_Profile_>> - View only the *Dive Profile* panel.
- <<S_ViewPanels,_Info_>> - View only the *Dive Notes* panel.
- <<S_ViewPanels,_Globe_>> - View only the *World Map* panel.
- _Yearly Statistics_ - Display summary statistics about dives during the last
year.
- _Prev DC_ - Switch to next dive computer.
- _Next DC_ - Switch to previous dive computer.
- _Full Screen_ - Toggles Full Screen mode.

=== Filter
- _Select Events_ - This option is not implemented yet.

=== Help
- _About Subsurface_ - Show a panel with the version number of _Subsurface_ as
well as licensing information.
- _Check for updates_ - Find out whether a newer version of Subsurface is available
on the http://subsurface.hohndel.org/[_Subsurface_ web site].
- _User Manual_ - Open a window showing this user manual.


== APPENDIX A: Operating system specific information for importing dive information from a dive computer.

=== Make sure that the OS has the required drivers installed
[icon="images/icons/drivers.jpg"]
[NOTE]
The operating system of the desktop computer needs the appropriate drivers in
order to communicate with the dive computer in whichever way the dive
computer prefers (e.g. bluetooth, USB, infrared).

	* On Linux users need to have the correct kernel
	  module loaded. Most distributions will do this automatically, so the
	  user does not need to load kernel modules. However, some communication
	  protocols require an additional driver, especially for rarely used
	  technology such as infrared.

	* On Windows, the OS should offer to download the correct
	  driver once the user connects the dive computer to the USB port and
	  operating system sees the equipment for the first time.

	* On a Mac users sometimes have to manually hunt for the correct
	  driver. For example the correct driver for the Mares Puck
	  devices or any other dive computer using a USB-to-serial interface
	  based on the Silicon Labs CP2101 or similar chip can be found as
	  _Mac_OSX_VCP_Driver.zip_ at the
http://www.silabs.com/support/pages/document-library.aspx?p=Interface&f=USB%20Bridges&pn=CP2101[Silicon Labs document and software repository].

[[S_HowFindDeviceName]]
=== How to Find the Device Name for USB devices and set its write permission
[icon="images/icons/usb.jpg"]
[NOTE]
When a user connects the dive computer by using a USB connector, usually
_Subsurface_ will either propose a drop down list that contains the
correct device name (or mount point for the Uemis Zurich), or it will
disable the device select drop down if no device name is needed at
all. In the rare cases where this doesn't work, here are some
instructions on ways to find out what the device name is:

.On Windows:

Simply try COM1, COM2, etc. The drop down list should contain all connected COM
devices.

.On MacOS:

The drop down box should find all connected dive computers.

.On Linux:

There is a definitive way to find the port:

 - Disconnect the USB cable from the dive computer
 - Open a terminal
 - Type the command: 'dmesg' and press enter
 - Plug in the USB cable of the dive computer
 - Type the command: 'dmesg' and press enter

A message similar to this one should appear:

	usb 2-1.1: new full speed USB device number 14 using ehci_hcd
	usbcore: registered new interface driver usbserial
	USB Serial support registered for generic
	usbcore: registered new interface driver usbserial_generic
	usbserial: USB Serial Driver core
	USB Serial support registered for FTDI USB Serial Device
	ftdi_sio 2-1.1:1.0: FTDI USB Serial Device converter detected
	usb 2-1.1: Detected FT232BM
	usb 2-1.1: Number of endpoints 2
	usb 2-1.1: Endpoint 1 MaxPacketSize 64
	usb 2-1.1: Endpoint 2 MaxPacketSize 64
	usb 2-1.1: Setting MaxPacketSize 64
	usb 2-1.1: FTDI USB Serial Device converter now attached to ttyUSB3
	usbcore: registered new interface driver ftdi_sio
	ftdi_sio: v1.6.0:USB FTDI Serial Converters Driver

The third line from the bottom shows that the FTDI USB adapter is
detected and connected to +ttyUSB3+. This information can now be used in
the import settings as +/dev/ttyUSB3+ which directs Subsurface to the correct
USB port.

Ensuring that the user has write permission to the USB serial port:

On Unix-like operating systems the USB ports can only be accessed by users who
are members
of the +dialout+ group. If one is not root, one may not be a member of
that group and
will not be able to use the USB port. Let us assume one's username is 'johnB'.

 - As root, type: +usermod -a -G dialout johnB+  (Ubuntu users: +sudo usermod
-a -G dialout johnB+)
This makes johnB a member of the +dialout+ group.
 - Type: +id johnB+     This lists all the groups that johnB belongs to and
verifies that
the appropriate group membership has been created. The +dialout+ group should
be listed
among the different IDs.

With the appropriate device name (e.g. +dev/ttyUSB3+) and with write permission
to the USB
port, the dive computer interface can connect and one should be able to import
dives.

[[S_HowFindBluetoothDeviceName]]
=== Setting up bluetooth enabled devices
[icon="images/icons/bluetooth.jpg"]
[NOTE]
For dive computers communicating through bluetooth like the Heinrichs
Weikamp Frog or the Shearwater Predator and Petrel there is a
different procedure to get the devices name to communicate with
_Subsurface_. Follow these steps:

 * *For the dive computer, after enabling Bluetooth, ensure it is in Upload mode.*

For Bluetooth pairing of the dive computer, refer to the
manufacturer's user guide. When using a Shearwater Predator/Petrel, select
_Dive Log -> Upload Log_ and wait for the _Wait PC_ message.

 * *Pair the _Subsurface_ computer with the dive computer.*

.On Windows:

Bluetooth is most likely already enabled. For pairing with the dive computer choose
_Control Panel->Bluetooth Devices->Add Wireless Device_.
This should bring up a dialog showing your dive computer (in Bluetooth mode) and
allowing pairing. Right click on it and choose _Properties->COM
Ports_ to identify the port used for your dive computer. If there are several
ports listed, use the one saying "Outgoing" instead of "Incoming".

For downloading to _Subsurface_, the _Subsurface_ drop-down list should contain
this COM port already. If not, enter it manually.

Note: If there are issues afterwards downloading from the dive computer using
other software, remove the existing pairing with the dive computer.

.On MacOS:

Click on the Bluetooth symbol in the menu bar and select _Set up
Bluetooth Device..._. The dive computer should then show up in the list of devices. Select it and go
through the pairing process. This step should only be needed once for
initial setup.

Once the pairing is completed the correct device is shown in the
'Device or Mount Point' drop-down in the _Subsurface_ *Import* dialog.

.On Linux
Ensure Bluetooth is enabled on the _Subsurface_ computer.
On most common distributions this should be true out of the box and
pairing should be straight forward. For instance, Gnome3 shows a
Bluetooth icon in the upper right corner of the desktop where one selects 'Set
up New Device'. This should show a dialog where one can select the
dive computer (which already should be in Bluetooth mode) and pair it.
If a PIN is required, try manually setting '0000'.

In the rare cases where the above is not true, then
depending on your system, try +initd+ or +systemd+. This might be different
and also involve loading modules specific to your hardware. In case your system
is running +systemd+, manually run +systemctl start bluetooth.service+ to
enable it, in case of +initd+, run something like +rc.config start bluetoothd+ or
+/etc/init.d/bluetooth start+.

One may also use a manual approach by using such commands:

 * +hciconfig+ shows the Bluetooth devices available on your
computer (not dive computer), most likely one will see a hci0, if not
try +hcitool -a+ to see inactive devices and  run +sudo
hciconfig hci0 up+ to bring them up.

 * +hcitool scanning+ gets a list of bluetooth enabled
client devices, look for the dive computer and remember the MAC
address are shown there

 * +bluez-simple-agent hci0 10:00:E8:C4:BE:C4+  pairs
the dive computer with the bluetooth stack of the _Subsurface_ computer, copy/paste
the MAC address from the output of 'hcitool scanning'

Unfortunately on Linux binding to a communication device has to be done
manually by running:

 * +rfcomm bind /dev/rfcomm0 10:00:E8:C4:BE:C4+ binds the dive
computer to a communication device in the desktop computer, in case rfcomm is
already taken use rfcomm1 or up. IMPORTANT: Copy/paste the MAC address
from the output of +hcitool scanning+, the MAC address shown above will not
work.

For downloading dives in _Subsurface_ specify the device name connected to the MAC
address in the last step above, e.g. _/dev/rfcomm0_.


== APPENDIX B: Dive Computer specific information for importing dive information.

[[S_ImportUemis]]
=== Import from a Uemis Zurich

[icon="images/icons/iumis.jpg"]
[NOTE]
_Subsurface_ downloads the information
stored on the SDA (the built-in file system of the Uemis) including
information about dive spots and
equipment. Buddy information is not yet downloadable.
Things are very similar to a normal USB-connected dive computer
(the Uemis is one of those that recharge when connected to the USB port).
The main difference is that one does not enter a
device name, but instead the location where the UEMISSDA file system is
mounted once connected to the dive computer. On Windows this is a drive letter (
often 'E:' or 'F:'), on a Mac this is
'/Volumes/UEMISSDA' and on Linux systems this differs depending on the
distribution. On Fedora it usually is
'/var/run/media/<your_username>/UEMISSDA'. In all cases _Subsurface_
should suggest the correct location in the drop down list.

After selecting the above device name, download the
dives from the Uemis Zurich. One technical issue with the Uemis Zurich
download implementation (this is a Uemis firmware limitation, not a
_Subsurface_ issue) is that one cannot download more than about 40-50
dives without running out of memory on the SDA. This will usually only
happen the very first time one downloads dives from the Uemis Zurich.
Normally when downloading at the end of a day or even after a dive
trip, the capacity is sufficient. If _Subsurface_ displays an error
that the dive computer ran out of space the solution is straight
forward.  Disconnect the SDA, turn it off and on again, and reconnect
it. You can now retry (or start a new download session) and the
download will continue where it stopped previously. One
may have to do this more than once, depending on how many dives are
stored on the dive computer.

[[S_ImportingGalileo]]
=== Importing dives from the Uwatec Galileo

[icon="images/icons/Galileo.jpg"]
[NOTE]
The Uwatec Galileo dive computers use infra red (IrDA) communication
between the dive computer and Subsurface. The Uwatec hardware uses
a USB dongle based on the serial infra-red (SIR) protocol and the
MSC7780 IrDA controller manufactured by MosChip
and marketed by Scubapro and some electronics companies.
Under Linux, the kernel
already provides for communication using the IrDA protocol. However,
the user additionally needs to load a driver for the IrDA interface
with the dive computer. The easiest way is to load the *irda-tools*
package from the http://irda.sourceforge.net/docs/startirda.html[Linux IrDA Project].
After the installation of the irda-tools, the *root user* can specify a device name
from the console as follows:
+irattach irda0+

After executing this command, Subsurface will recognise the Galileo
dive computer and download dive information.

Under Windows, a similar situation exists. Drivers for the MCS7780 are
available from some Internet web sites e.g.
http://www.drivers-download.com/Drv/MosChip/MCS7780/[www.drivers-download.com].

For the Apple Mac, IrDA communication via the MCS7780 link is not
available for OSX 10.6 or higher.

[[S_ImportingDR5]]
=== Importing dives from Heinrichs Weikamp DR5

[icon="images/icons/HW_DR5.jpg"]
[NOTE]
When mounted as a USB drive the Heinrichs Weikamp DR5 saves a single UDDF file
for every dive.
Mark all the dives you'd like to import or open.
Note: The DR5 does not seem to store gradient factors nor deco information, so
for _Subsurface_ it is not possible to display them. Adjust the gradient
factors in the _Tec Settings_ in _Subsurface_ to generate a deco overlay in the
_Subsurface_ *Dive Profile* panel but please note that the deco calculated by
_Subsurface_ will most likely differ from the one displayed on the DR5.

=== Import from Shearwater Predator using Bluetooth

[icon="images/icons/predator.jpg"]
[NOTE]
Using a Shearwater Predator one may be able to pair Bluetooth but then encounter
issues when downloading, showing errors like _Slip RX: unexp. SLIP END_ on the
Predator.
This might also arise when using other dive log software and operating
systems other than Linux. We have no detailed idea about the source and how to fix
this, but it is reported to be solved sometimes by one of these steps:

 * use the Bluetooth dongle which came with the Shearwater Predator instead of
   the built-in one of the _Subsurface_ computer
 * switch to different Bluetooth drivers for the same hardware
 * switch off WiFi while using Bluetooth


== APPENDIX C: Exporting Dive log information from external dive log software.

The import of dive log data from external dive log software is mostly performed
using
the dialogue found by selecting _Import_ from the Main Menu, then clicking on
_Import Log Files_. This is a single-step process, more information about which
can be found
xref:Unified_import[here.]
However, in some cases, a two-step process may be required:

1. Export the foreign dive log data to format that is accessible from
_Subsurface_.
2. Import the accessible dive log data into _Subsurface_.

This appendix provides some information about approaches to export dive log
data from foreign
dive log software. The procedures below mostly apply to Linux and/or Windows.

[[S_ImportingDivesSuunto]]
=== Exporting dives from *Suunto Divemanager (DM3 and DM4)*
[icon="images/icons/suuntologo.jpg"]
[NOTE]
Divemanager 3 (DM3) is an older version of the Suunto software. More recent
Suunto dive computers use Divemanager 4 (DM4). The
two versions of Divemanager use different methods and different file naming
conventions to export dive log data.

*Divemanager 3 (DM3):*

1. Start 'Suunto Divemanager 3' and log in with the name containing the logs
2. Do not start the import wizard to import dives from the dive computer.
3. In the navigation tree on the left side of the program-window, select the appropriate
dives.
4. Within the list of dives, select the dives you would like to import later:
	* To select certain dives: hold 'ctrl' and click the dive
	* To select all dives:  Select the first dive, hold down shift and
select the
last dive
5. With the dives marked, use the program menu _File -> Export_
6. The export pop-up will show. Within this pop-up, there is one field called 'Export Path'.
	* Click the browse button next to the field Export Path
		** A file-manager like window pops up
		** Navigate to the directory or storing the
Divelog.SDE file
		** Optionally change the name of the file for saving
		** Click 'Save'
	* Back in the Export pop-up, press the button 'Export'
7. The dives are now exported to the file Divelogs.SDE.

*Divemanager 4 (DM4):*

To export divelog from 'Suunto DM4', one needs to locate the DM4 database
where the dives are stored. the user can either look for the original
database or make a backup of the dives. Both methods are described here.

Locating the Suunto DM4 database:

1. Start Suunto DM4
2. Select 'Help -> About'
3. Click 'Copy' after text 'Copy log folder path to clipboard'
4. Now open Windows Explorer
5. Paste the address to the path box at the top of the File Explorer
6. The database is called DM4.db

Backing up Suunto DM4:

1. Start Suunto DM4
2. Select 'File - Create backup'
3. From the file menu select the location and name for the backup, we'll
   use DM4 in here with the default extension .bak
4. Click 'Save'
5. The dives are now exported to the file DM4.bak


=== Exporting from Mares Dive Organiser V2.1
[[Mares_Export]]

[icon="images/icons/mareslogo.jpg"]
[NOTE]
Mares Dive Organiser is a Microsoft application. The dive log is kept as a
Microsoft SQL Compact Edition data base with a '.sdf' filename extension. The
data base includes all Dive Organiser-registered divers on the particular
computer and all Mares dive computers used. The safest way to obtain a copy
of the dive data base is to export the information to another compatible format
which can be imported into _Subsurface_.

1. Within Dive Organiser, select
_Database -> Backup_ from the main menu and back up the data base to the desk
top.
This creates a zipped file DiveOrganiserxxxxx.dbf.
2. Rename the file to
DiveOrganiserxxxxx.zip. Inside the zipped directory is a file
_DiveOrganiser.sdf_.
3. Extract the _.sdf_ file from the zipped folder to your Desktop.

[[S_ImportingDivinglog]]
=== Exporting dives from *DivingLog 5.0*

[icon="images/icons/divingloglogo.jpg"]
[NOTE]
Unfortunately DivingLog XML files give us no
indication on the preferences set on one's system. So in order for
_Subsurface_ to be able to successfully import XML files from DivingLog
one first needs to ensure that DivingLog is configured
to use the Metric system (one can easily change this within Diving Log by
selecting 'File -> Preferences -> Units and Language' by clicking the 'Metric'
button). Then do the following:

1. In Divinglog open the 'File -> Export -> XML' menu
2. Select the dives to export
3. Click on the export button and select the filename


== APPENDIX D: FAQs.

=== Subsurface appears to miscalculate gas consumption and SAC
[[SAC_CALCULATION]]
'Question': I dived with a 12.2 l tank, starting with 220 bar and ending with 100 bar, and I calculate a different SAC compared what _Subsurface_ calculates. Is _Subsurface_
miscalculating?

'Answer': Not really. What happens is that _Subsurface_ actually calculates gas
consumption differently - and better - than you expect.
In particular, it takes the incompressibility of the gas into account.
Traditionally, Gas consumption and SAC should be:
+consumption = tank size x (start pressure - end pressure)+

and that's true for an ideal gas, and it's what you get taught in dive theory.
But an "ideal gas" doesn't actually exist, and real gases actually don't compress
linearly with pressure. Also, you are missing the fact that one atmosphere of
pressure isn't actually one bar.
So the *real* calculation is:

+consumption = (amount_of_air_at_beginning - amount_of_air_at_end)+

where the amount of air is *not* just "tank size times pressure in bar".
It's a combination of: "take compressibility into account" (which is a fairly
small issue under 220 bar - you'll see more differences when you do high-pressure
tanks with 300bar) and "convert bar to atm" (which is the majority of your discrepancy).
Remember: one ATM is ~1.013 bar, so without the compressibility, your gas use is:

+12.2*((220-100)/1.013)+

which is about 1445, not 1464. So there was 19 l too much in your simple
calculation that ignored the difference between 1 bar and one ATM.
The compressibility does show up above 200 bar, and takes that 1445 down
about eight liters more, so you really did use only about 1437 l of air at surface pressure.

So be happy: your SAC really is better than your calculations indicated.
Or be sad: your cylinder contains less air than you thought it did.
And as mentioned, the "contains less air than you thought it did" really
starts becoming much more noticeable at high pressure. A 400 bar really does not
contain twice as much air as a 200 bar one. At lower pressures, air acts pretty much like an ideal gas.

=== Some dive profiles have time discrepancies with the recorded samples from my dive computer...

_Subsurface_ ends up ignoring surface time for many things (average depth, divetime, SAC, etc).
 For example, if you end up doing a weight check (deep enough to trigger the "dive started")
but then come back up and wait five minutes for your buddies, your dive computer may say
that your dive is 50 minutes long - because you have fifty minutes worth of samples - but
subsurface will say it's 45 minutes - because you were actually diving for 45 minutes.
It's even more noticeable if you do things like divemastering the initial OW dives, when
you may stay in the water for a long time, but spend most of it at the surface. And then
 you don't want that to count as some kind of long dive”.