Radio Compass Bearing Indicator Type MN-40E
Here is a good example of a Radio Compass Bearing Indicator, Type MN-40E, The face and its use is very similar in appearance to the I-82-A indicator of a number of radio compass systems used during and after WWII. The Bendix data label does not contain any recognizable US military markings and may have been for a civil/commercial aircraft.
The indicator was connected via flexible mechanical cable to a rotatable loop antenna mounted either on the top or below the aircraft. The antenna seeks a signal from a known ground station, whereas when the loop is positioned perpendicular to the source of the signal the signal is strongest, thus the aircraft's position relative to the ground station can be determined.
The instrument is in superb condition and may never have been installed. Measures ~5 inches x ~2 inches.