1 files changed, 3 insertions, 2 deletions
diff --git a/dive.h b/dive.h
index a5c760640..f06791cc5 100644
--- a/dive.h
+++ b/dive.h
@@ -134,9 +134,10 @@ static inline int interpolate(int a, int b, int part, int whole)
 	return rint(x / whole);
 }
 
-static inline depth_t gas_mod(struct gasmix *mix, pressure_t po2_limit) {
+/* MOD rounded to multiples of roundto mm */
+static inline depth_t gas_mod(struct gasmix *mix, pressure_t po2_limit, int roundto) {
 	depth_t depth;
-	depth.mm = po2_limit.mbar * 1000 / get_o2(mix) * 10 - 10000;
+	depth.mm = ((po2_limit.mbar * 1000 / get_o2(mix) * 10 - 10000) / roundto) * roundto;
 	return depth;
 }