Added the gravitational potential as one of the default unit conversion schemes.

src/units.c

@@ -220,6 +220,11 @@ void units_get_base_unit_exponants_array(float baseUnitsExp[5],
       baseUnitsExp[UNIT_TIME] = -2.f;
       break;
 
+    case UNIT_CONV_POTENTIAL:
+      baseUnitsExp[UNIT_LENGTH] = 2.f;
+      baseUnitsExp[UNIT_TIME] = -2.f;
+      break;
+
     case UNIT_CONV_FORCE:
       baseUnitsExp[UNIT_MASS] = 1.f;
       baseUnitsExp[UNIT_LENGTH] = 1.f;

src/units.h

@@ -73,6 +73,7 @@ enum unit_conversion_factor {
   UNIT_CONV_DENSITY,
   UNIT_CONV_SPEED,
   UNIT_CONV_ACCELERATION,
+  UNIT_CONV_POTENTIAL,
   UNIT_CONV_FORCE,
   UNIT_CONV_ENERGY,
   UNIT_CONV_ENERGY_PER_UNIT_MASS,