His was used in various radio set-ups and testing units, specifically in conjunction with the Me262 Turbo Jet Fighter Aircraft! This item indicated the current amperage of the aircraft radio electrical system. Electric currents are measured in amperes (A), hence the name.
For direct measurement, the ammeter is connected in series with the circuit in which the current is to be measured. An ammeter usually has low resistance so that it does not cause a significant voltage drop in the circuit being measured. Made of brass, steel, and aluminum, this item is of late-war manufacture (circa 1944).
Brought back by a US Serviceman, it does feature various marks, scratches, and wear, but it does not detract. I know this was used in conjunction with the Me262, however, I have not been able to find it in the any cockpit version. Could have been used for ground testing and calibration. I have not tested it. Would make a VERY RARE addition to any collection or display!