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diff --git a/Documentation/user-manual.txt b/Documentation/user-manual.txt index 2a0dc6cb3..5ed500849 100644 --- a/Documentation/user-manual.txt +++ b/Documentation/user-manual.txt @@ -1811,6 +1811,67 @@ air diving at a depth equalling the END. Figure (*B*) above shows an information box with a nearly complete set of data. +==== The Gas Pressure Bar Graph + +On the left of the *Information Box* is a vertical bar graph indicating the +pressures of the nitrogen (and other inert gases, e.g. helium, if applicable) that the diver +was inhaling _at a particular instant during the dive_, indicated by the position +of the cursor on the *Dive Profile*. The drawing on the left below indicates the +meaning of the different parts of the Gas Pressure Bar Graph. + +image::images/GasPressureBarGraph.jpg["FIGURE:Gas Pressure bar Graph",align="center"] + +- The light green area indicates the total gas, with the top margin of the light green +area indicating the total gas pressure inhaled by the diver and measured from the bottom +of the graph to the top of the light green area. This pressure has a _relative_ value in the graph +and does not indicate absolute pressure. + +- The horizontal black line underneath the light green margin indicates the equilibrium pressure +of the inert gases inhaled by the diver, usually nitrogen. In +the case of trimix, it is the pressures of nitrogen and helium combined. In this example, +the user is diving with EAN32, so the inert gas pressure is 68% of the distance from the +bottom of the graph to the total gas pressure value. + +- The dark green area at the bottom of the graph represents the pressures of inert gas in each +of the 16 tissue compartments, following the Bühlmann algorithm, the fast tissues being on the +left hand side. + +- The top black horizontal line indicates the the gradient factor that applies to the depth of +the diver at the particular point on the *Dive Profile*. The appropriate gradient factor is an +interpolation between the FGLow and GFHigh values specified in the Graph tab of the *Preferences +Panel* of *Subsurface*. + +- The bottom margin of the red area in the graph indicates the Bühlman-derived M-value, that is the +pressure value of inert gases at which bubble formation is expected to be severe, resulting +in decompression sickness. + +These five values are indicated on the left in the graph above. The way the Gas Pressure Bar Graph changes +during a dive is indicated on the right hand side of the above figure for a diver using EAN32. + +- Graph *A* indicates the situation at the start of a dive with diver at the surface. The pressures in all +the tissue compartments are still at the quilibrium pressure because no diving has taken place. + +- Graph *B* indicates the situation after a descent to 30 meters. Few of the tissue compartments have had +time to respond to the descent, their gas pressures being far below the equilibrium gas pressure. + +- Graph *C* represents the pressures after 30 minutes at 30 m. The fast compartments have attained +equilibrium (i.e. they have reached the hight of the black line indicating the equilibrium pressure). The +slower compartments (towards the right) have not reached equilibrium and are in the process of slowly +increasing in pressure. + +- Graph *D* shows the pressures after ascent to a depth of 4.5 meters. Since, during ascent, the total +inhaled gas pressure has decreased strongly from 4 bar to 1.45 bar, the pressures in the different tissue +compartments now exceed that of the total gas pressure and approaches the gradient factor value (i.e. +the top black horizontal line). Further ascent will result in exceeding the gradient +factor value (GFHigh), endangering the diver. + +- Graph *E* indicates the situation after remaining at 4.5 meters for 10 minutes. The fast compartments +have decreased in pressure. As expected, the pressures in the slow compartments have not changed much. +The pressures in the fast compartments do not approach the GFHigh value any more and the diver is safer +than in the situation indicated in graph *D*. + + + == Organising the logbook (Manipulating groups of dives) === The Dive List context menu |