Tachometer, Sensitive, Electric, US Navy
This is a Sensitive Electric Tachometer, made by Bendix, part number 2234YZA9-28-A1, as Federal Stock number R88-I-2385-100 for aircraft of the US Navy both during and after WWII. Aircraft which used this tachometer included the US Navy fighters F4U-5 Corsair (per its Parts Manual April 1951) and F8F Bearcat (per its Erection and Maintenance Manual March 1948). It has also been identified visually in cockpit illustrations in the flight manuals of the patrol aircraft PBY-5 Catalina and the dive bomber SB2C Helldiver. See photo of F4U Corsair from its Flight Manual dated 1945 showing the location of the tachometer.
As the tachometer received an electric signal from the engine-mounted sensor, the RPM's were indicated by the rotating pointer on the dial. The numerical digits along the perimeter of the dial indicate RPM in 000's, and with each 360 degree clockwise rotation of the pointer, the RPM 0,000's would be displayed in the small window at the 9 o'clock position. The total RPM's are the combination of the thousands displayed in the window plus the corresponding numerical location of the pointer. It is called 'sensitive' because it displays RPMs at a finer resolution than tachometers that only rotate once to display the full RPM range.
The tachometer is definitely 'experienced' but is in reasonable condition given its age. The electrical connection in the back has been removed, and there is a small dent in the rim of the face. The glass and case are intact and the dial lettering is clear and legible.