Suction Gage, AN 5771-5, US Army Air Force WWII C-47 It is a hand held

It is a hand held finder used to ascertain the range of an enemy aircraft based upon its known wingspan

Unfortunately

Its face has embossed "BU AERO USN" i

the difference between the totals is the difference in density of the two fuel types

It has a service label from the US Air Force Tinker Air Base's OCAMA (Oklahoma City Air Materiel Area)

Suction Gage, AN 5771-5, US Army Air Force WWII C-47 It is a hand heldThis is a WWII era Suction Gage, AN 5771 5, made by Collens. This indicator has a serial number prefix "AF 43", evidence of a manufacturing year 1943. The AN 5771 5 Suction Gage was used across all aircraft of the US Army Air Corps, including bombers B 17, B 24, B 25, fighters P 38, P 40, P 47, P 51, and transport C 47. The Suction Gage measured the amount of vacuum generated to power the pneumatically operated gyroscopic instruments, such as the Gyro