JAPANESE AIRPLANE AIR PRESSURE GAUGE

From my collection of Japanese Airplane parts. I am taking a guess at this pressure gauge that it is for the pilot to control oxygen to his face mask. I am guessing at this because it appears to screw onto a bottle, and two it has a slip on fitting for a rugger hose and what appears to be an on and off turn switch. So having said that i don't have any idea what it is for, so someone can verify or give us the correct information. Th gauge is 2 1/4" high and 2 1/2" wide, it is well marked with the original makers tag and the turn dial is also marked in two different positions.. Condition very good +++