Master Compass Indicator, Flux Gate Compass System AN5752-2
The Master Compass Indicator AN5752-2 was an integral component of the WWII era Bendix Gyro Flux Gate Compass System used in aircraft such as the B-17, B-24, and B-29.
The 7-component Flux Gate Compass system was designed to provide accurate navigational guidance using the earth's magnetic forces by minimizing interference from the systems of the aircraft, such as its turrets, guns, and engines. A flux gate gyro transmitter typically located within the wing would send signals to the Master Compass Indicator normally located in the navigator's compartment, which in turn would transmit these signals to smaller repeater indicators located at other positions such as the pilots instrument panel. See photos in the gallery describing the system in greater detail.
The knob at the top of the indicator is actually a hex key used to adjust deviations in readings on the Master Compass. Once turned and removed, the perimeter face plate is removed, revealing set screws around the face. These set screws may then be used to correct the reading of the indicator. The knob at the bottom is used to adjust variation.
This example is in reasonably-good condition given its age. It has a service label marked NAS JAX (Naval Air Station Jacksonville FL) dated 1952. The housing had been repainted at one point, and has a small crack along the bottom, see photo. The face is in perfection condition. Measures 6 inches diameter by ~8 inches deep.