Engine Pressure Ratio Indicator B-24 The F marker was set

The F marker was set to the desired Acceleration Altitude

should the ball turret gunner hear "bandit at 4 o'clock low"

mso-pagination:widow-orphan

and was likely used on a US Air Force or US Navy aircraft during the 1950's

The mach number limit is adjusted for the specific aircraft model by turning the inset screw on the rear case prior to installation

Engine Pressure Ratio Indicator B-24 The F marker was setHere is a 1950 60's era Engine Pressure Ratio Indicator made by AiResearch. EPR indicators were used in jet engine aircraft. The glass is slight cracked at the 2 3 o'clock position. Measures ~2 inches diameter and ~5 inches deep. See photos.