Radio Compass Bearing Indicator Type MN-40E Piasecki By viewing the target through

By viewing the target through the device and turning the knob until the presumed height of the known target is bracketed between the upper and lower limiters in the viewfinder

It is specifically labeled for use in aircraft of the US Air Force

The Fl number is illegible

Advanced with Radio Aids (TO 30-100B-1

Sperry part number 644836

Radio Compass Bearing Indicator Type MN-40E Piasecki By viewing the target throughHere 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