Fractional control: Enable player to pressurise rooms by fractions. This allows players to go to a vent, set the vent to depressurize to a minimum value (i.e. a value by which the pressure will go no lower) and a maximum value to which it will pressurize, but pressurize no further. This can be used to: A) refill oxygen tanks at a controllable rate B) discharge oxygen at a controllable rate C) enable players to effectively ration oxygen in a ship when running low. Alternate uses also allow ships in space, with large cargo holds, to test the efficiency of small ships inside with atmospheric thrusters, to see how they perform at various altitudes.