Precipitation Static, USAAF Manual No. 10 Dec 1944 SBD Dauntless They were essentially timers for

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

The single pointer and course setting arrow rotate

The Army type E-9 tachometer indicator consists of a three phase alternating current  synchronous motor and an indicating element

The other volumes were Airplane General

Here is WWII-era vacuum-driven Gyro Horizon Indicator Type AN-5736-1

Precipitation Static, USAAF Manual No. 10 Dec 1944 SBD Dauntless They were essentially timers forThis is an original training manual covering the topic of Precipitation Static published by the US Army Air Corps in 1944 for use in training pilots. The manual discusses the build up of static charge on the aircraft in flight during different atmospheric conditions and how this affects radio receiving equipment. This 36 page manual is in good condition given its age. It came to us from the estate of a B 17 flight instructor.