Compass, Aperiodic, US Navy Aviation, 88-C-845 (Type D-12) Bf-109 They were essentially timers for

They were essentially timers for communications radios that broadcast a fourteen second carrier wave every minute

such as torpedo bomber TBM Avenger (see image from TBM Flight Manual)

As the airspeed increases

but this has not been confirmed

It also depresses much like it would for a stopwatch

Compass, Aperiodic, US Navy Aviation, 88-C-845 (Type D-12) Bf-109 They were essentially timers forThe US Navy 88 C 845 (USAAF Type D 12) Direct Reading Aperiodic Navigational Compass was used at the navigators station across many US Navy WWII aircraft, including patrol bombers PBY Catalina, PB2Y Coronado, PB4 Privateer, PV 1 Ventura and PV 2 Harpoon. Made by Bendix, part number 1828 1 A. The navigators' direct reading compass is known as an aperiodic (without a period) compass, since the needle returns to rest quickly and without appreciable