The heading indicator works using a gyroscope, tied by an erection mechanism to the aircraft yawing plane, i. e. the plane defined by the longitudinal and the transverse axis of the aircraft. As such, any configuration of the aircraft yawing plane that does not match the local Earth horizontal results in an indication error. The heading indicator is arranged such that the gyro axis is used to drive the display, which consists of a circular compass card calibrated in degrees. The gyroscope is spun either electrically, or using filtered air flow from a suction pump (sometimes a pressure pump in high altitude aircraft) driven from the aircraft's engine. Because the Earth rotates, and because of small accumulated errors caused by imperfect balancing of the gyro, the heading indicator will drift over time (real drift), and must be reset using a magnetic compass periodically.

The type C-5C indecator as appeared in the US Air Force Boeing B-52 E&F Stratofortress Bomber as well as the Lockheed C-130B Hercules Transport of the 1950-60's. The serial # starts "AF 55" likely indicating a manufacturing date for a USAF order during 1955. Based on info i could find... It is possible that it was in use of other aircraft of the same era.