February 17, 2014 at 8:46 pm
A friend of mine has one of these. Probably American. Can anyone throw any light? Edit, Case says U.S. AIR FORCE part number A898RS test unit on the case.
Ta in advance.

By: sopwith.7f1 - 18th February 2014 at 11:31
Rough guess would be magneto RPM drop tester for something like a Kinner engined aircraft.
Bob T.