Tachometer, Electric, US Navy Mark V, 88-I-2500 TBM Avenger
This is a WWII-era single engine, electrical, aircraft tachometer Mark V made by Kollsman under contract for the US Navy, part number 621KN-04, FSSC number 88-I-2500. This tachometer was the type used in the infamous USN carrier-based TBM Avenger torpedo bomber according to the TBM Erection & Maintenance Manual dated 1945. See the illustration of the instrument panel from the TBM-3 Flight Manual dated 1945 showing the location of the tachometer.
RPM in 100's is indicated on the outer scale. RPM in 1000's is indicated on the inner scale. As the engine speed increased, the large pointer rotated clockwise. As it passes the 12 o'clock position, the smaller pointer would indicate the RPM in 1000's. This is a 'sensitive' tachometer in that it provides more precise resolution of the engine speed vs those with a single pointer for the full RPM range.
The glass is clear and the lettering is precise. There is some dust under the glass that could be opened and cleaned. There are some remnants of the zinc oxide paint on the rim of the face that would have been picked up from the rear of the metal instrument panel when it was removed. It is an exceptional specimen. Measures 3.25 inches diameter and ~5 inches deep.