Oxygen Flow Indicator, MK III, British Royal Air Force, 1942 A-26 For example

For example

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

This tachometer has a serial number prefix of AC 41

as used in A-1 Skyraider (middle flag missing)

Oxygen Flow Indicator, MK III, British Royal Air Force, 1942 A-26 For exampleHere is a WWII era artifact: an Oxygen Flow Indicator, Mk III, Stores Reference 6D 430. Multi crew RAF aircraft had these installed at crew stations, such as gun turrets, radio operator, navigator, etc., to indicate the gross flow (not the precise rate) of oxygen from the primary oxygen tanks (not portables) to the local junction at each station. Commonly used in aircraft such as the Lancaster, Wellington, Stirling, Mosquito, etc. The serial number on