Gilson Bearing Averager

Data:

• The device was apparently manufactured for the U.S. Navy.
• It has a mechanical linkage that finds the midway point between two compass bearings. Not a weighted average, just the midpoint.
• Also, the range of allowed inputs is limited: max spread angle is 70°

Questions:

1. What might be the purpose of the device? Its construction seems too complicated to justify the limited calculations of which it is capable. Even if a sailor were not skilled with numbers and could use a device to assist with simple nautical calculations, what would be the purpose of a device that only calculates a simple, unweighted average of two numbers, and only over a limited range?
   If the two values straddle 360°, errors in mental averaging are more probable, especially in stressfull situations.
   Could it be a teaching aid? Students at West Point and the Naval Academy used several simplified instruments. D.L. Hilton
   Course corrector? Fred Stahl
   What about the concentric circles? Could one plot on the device?
   It is submarine-related? See this thread about tracking submarines Wayne R Pinnow
   Torpedo's?
   On 2nd thought if it was for torpedoes I think it would need a distance indicator to be of any use. If it was for averaging a rolling ship's true aim (my first thought) wouldn't that make sense? Ace Hoffman
   Torpedo calculators are usually somewhat more complex. See also Steger, 1925 and Pitkin, 1947 Andries de Man
   What can be deduced from (the format of) the Purchase Number N5 SR 7668-P ?