Oxygen Regulator Type A-9A S2 Tracker The manual is 950 pages

The manual is 950 pages and ~2inches thick

In the center of the bowl is a semi-float type card to which are attached the magnetized needles and the radial arms

operates in the same manner but has greater air volume capacity for larger aircraft with more air-driven instruments such as a heavy bomber or transport

with a serial number prefix of AC-39

Oxygen Regulator Type A-9A S2 Tracker The manual is 950 pagesThis is a WWII era aircraft Oxygen Regulator Type A 9A as used across bomber and transport aircraft of the US Army Air Force and US Navy, such as the B 17 Flying Fortress (see image illustrating the location of the co pilot's regulator from the B 17F flight manual dated 1943). This example has a serial number prefix of AC41, evidence of a year of manufacture of 1941. The A 9A regulator was a low pressure continuous flow regulator (vs the on demand,