Compass, Aperiodic, US Army Air Force Type D-12 Victor The knurled center knob was

The knurled center knob was then tightened to secure it in place

or film spools

The co-pilot would select the tank to view by rotating the knob

See diagram from the UH-1 Flight Manual

and the markings on the face are in place (yet changing color from the many years) and unblemished

Compass, Aperiodic, US Army Air Force Type D-12 Victor The knurled center knob wasThe US Army Air Force Type D 12 Direct Reading Aperiodic Compass was used at the navigators station across many US WWII aircraft, including heavy bombers B 17, B 24, B 29, medium bombers B 25 and B 26, and transports C 46, C 47, and C 54. Made by Bendix, part number 1832 1 A, it has a serial number prefix of AF 45, indicative of a manufacturing year 1945. The navigators' direct reading compass is known as an aperiodic (without a period) compass, since