diff --git a/equipment.c b/equipment.c
index 6d09e6fab..51020e5a3 100644
--- a/equipment.c
+++ b/equipment.c
@@ -241,7 +241,7 @@ void reset_cylinders(struct dive *dive)
 		if (cylinder_none(cyl))
 			continue;
 		if (cyl->depth.mm == 0) /* if the gas doesn't give a mod, assume conservative pO2 */
-			cyl->depth = gas_mod(&cyl->gasmix, pO2, 3000);
+			cyl->depth = gas_mod(&cyl->gasmix, pO2, M_OR_FT(3,10));
 		if (cyl->type.workingpressure.mbar)
 			cyl->start.mbar = cyl->end.mbar = cyl->type.workingpressure.mbar;
 		cyl->gas_used.mliter = 0;
diff --git a/helpers.h b/helpers.h
index 392dcb5ac..4d9684e9c 100644
--- a/helpers.h
+++ b/helpers.h
@@ -35,8 +35,6 @@ QString get_trip_date_string(timestamp_t when, int nr);
 QString uiLanguage(QLocale *callerLoc);
 void selectedDivesGasUsed(QVector<QPair<QString, int> > &gasUsed);
 
-#define M_OR_FT(_m, _f) ((prefs.units.length == units::METERS) ? ((_m) * 1000) : (feet_to_mm(_f)))
-
 #if defined __APPLE__
 #define TITLE_OR_TEXT(_t, _m) "", _t + "\n" + _m
 #else
diff --git a/qt-ui/diveplanner.cpp b/qt-ui/diveplanner.cpp
index 57438eb39..0708b6aef 100644
--- a/qt-ui/diveplanner.cpp
+++ b/qt-ui/diveplanner.cpp
@@ -694,7 +694,7 @@ bool DivePlannerPointsModel::addGas(struct gasmix mix)
 			 * The user should be able to change this depth manually. */
 			pressure_t modpO2;
 			modpO2.mbar = prefs.decopo2;
-			cyl->depth = gas_mod(&mix, modpO2, 3000);
+			cyl->depth = gas_mod(&mix, modpO2, M_OR_FT(3,10));
 
 			CylindersModel::instance()->setDive(stagingDive);
 			return true;
diff --git a/qt-ui/models.cpp b/qt-ui/models.cpp
index a5a1f5bff..823619f64 100644
--- a/qt-ui/models.cpp
+++ b/qt-ui/models.cpp
@@ -251,7 +251,7 @@ bool CylindersModel::setData(const QModelIndex &index, const QVariant &value, in
 			cyl->gasmix.o2 = string_to_fraction(vString.toUtf8().data());
 			pressure_t modpO2;
 			modpO2.mbar = prefs.decopo2;
-			cyl->depth = gas_mod(&cyl->gasmix, modpO2, 3000);
+			cyl->depth = gas_mod(&cyl->gasmix, modpO2, M_OR_FT(3,10));
 			changed = true;
 		}
 		break;
diff --git a/subsurface.pro b/subsurface.pro
index 86d19cd71..3dec531c2 100644
--- a/subsurface.pro
+++ b/subsurface.pro
@@ -35,6 +35,7 @@ HEADERS = \
 	profile.h \
 	qt-gui.h \
 	qthelper.h \
+	units.h \
 	divecomputer.h \
 	qt-ui/about.h \
 	qt-ui/completionmodels.h \
diff --git a/units.h b/units.h
index 4b32d5237..a8c0d7dbc 100644
--- a/units.h
+++ b/units.h
@@ -16,6 +16,12 @@ extern "C" {
 #define SURFACE_PRESSURE_STRING "1013"
 #define ZERO_C_IN_MKELVIN 273150 // mKelvin
 
+#ifdef __cplusplus
+#define M_OR_FT(_m, _f) ((prefs.units.length == units::METERS) ? ((_m) * 1000) : (feet_to_mm(_f)))
+#else
+#define M_OR_FT(_m, _f) ((prefs.units.length == METERS) ? ((_m) * 1000) : (feet_to_mm(_f)))
+#endif
+
 /* Salinity is expressed in weight in grams per 10l */
 #define SEAWATER_SALINITY 10300
 #define FRESHWATER_SALINITY 10000