Ammeter Strommesser Luftwaffe Fl32509-4 A4 Skyhawk the top compass card would

the top compass card would rotate to match the heading on the bottom card

According to Flight Magazine dated 1957

a small alternator

since it has Russian Cyrillic lettering on its face

Also common to the British version is the stamped statement "Do Not Jar Handle Like Eggs"

Ammeter Strommesser Luftwaffe Fl32509-4 A4 Skyhawk the top compass card wouldThis is a WWII era aircraft Ammeter (Strommesser) Fl 325509 4, as used in aircraft of the German Luftwaffe. It is 1 3 4" diameter, and 1 3 4" deep mounted in a black, steel cylinder by two small slotted screws. It has a movable pointer to indicate the current in an electrical circuit. There is a "0" above an "A" at center position flanked by a "L" and a "E" to the left and right of the scale, likely indicating negative or positive draw. stamped in