Tachometer, Air Ministry, Mk IA, 6C/223 (Serial 134/42) C-43 25 inches diameter by 5

25 inches diameter by 5 inches deep

and then from 2500-3500 as the pointer continues past the 12 o'clock position and read along the inner scale to the 4 o'clock position

The pointers are marked L and R

the drift angle is determined by reading the location of the pointer on the base's scale

Tachometer, Air Ministry, Mk IA, 6C/223 (Serial 134/42) C-43 25 inches diameter by 5Here is a WWII era Mk IA chronometric (mechanical) tachometer of the British Royal Air Force, Air Ministry stores reference number 6C 223, serial number 134 42. This tachometer measures from 500 to 5000 RPM, and has a totalizing counter which measures up to the millions of RPM. The "6C" prefix in the stores reference number indicates that this tachometer was intended as a test instrument, and the "42" in the serial number indicates a manufacturing