Radio Transmitter BC-459-A, of US Army Air Force & Navy SCR-274N, AN/ARC-5 Command Sets B-57 see photo from its flight

see photo from its flight manual dated 1944 showing the indicator

The temp reading is inaccurate

all for the elimination of errors caused by magnetism

The manual appears to be complete with hundreds of pages of text

An exceptional find

Radio Transmitter BC-459-A, of US Army Air Force & Navy SCR-274N, AN/ARC-5 Command Sets B-57 see photo from its flightThe BC 459 A Radio Transmitter was part of the WWII era US Army Air Force's SCR 274N "Command Set" (also used in the US Navy's ATA ARA and the later AN ARC 5 communication system where it was designated T 22 ARC 5). Frequency range is 7 9. 1 MHz. According to the Airborne Radio Equipment Manual of the Signal Section Air Service Command Dated April 1943, the SCR 274N was used in bombers B 17, B 24, B 25, B 26, and A 20, fighters P 38, P 39, P 40, and P