Tachometer, Electric, US Navy, R-88-I 2385-100 F4U Corsair
This is a single engine, electrical, aircraft tachometer made by General Electric under contract for the US Navy, part number 8DJ13AFF, FSSC number 88-I-2385-100. This tachometer was the type used in the WWII-era USN carrier-based F4U-5 fighter according to the F4U-5 Erection & Maintenance Manual dated 1948, as well as in the post WWII-era USN F8F fighter according to its Erection & Maintenance Manual also dated 1948. See the illustration of the instrument panel from the F4U-5 Erection and Maintanance Manual 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. The last aircraft to host this instrument apparently had a redline RPM level of ~3,000, as this limit was marked on the inner scale by a technician. It also has a service label from Naval Air Rework Facility (NARF) Pensacola FL. It is an exceptional specimen. Measures 3.25 inches diameter and ~4 inches deep.