Cowl Flap Position Indicator, Bendix Magnesyn, C-121 Lockheed Constellation P-51 likely used by the US

likely used by the US military during the 1940-50s: AC 0-30 Volts

and the internal mechanism can be removed to reveal the electrical gyroscope

as appeared in aircraft such as the Grumman S2E Tracker and Lockheed P2V-7 Neptune Antisubmarine Warfare aircraft (according to their flight manuals

not gallons

The cover can be removed to reveal the gyro inside

Cowl Flap Position Indicator, Bendix Magnesyn, C-121 Lockheed Constellation P-51 likely used by the USThis is a dual Cowl Flap Position indicator as used in the US Air Force C 121 transport version of the Lockheed Constellation. See photo of the location of the instrument on the Flight Engineers upper instrument panel from the C 121 flight manual dated 1958. It has a date stamp of Dec 1956 on the side case. Measures 3. 25 inches diameter and ~3 inches deep.