Helicopter Dual Tachometer Kollsman 981BX-8-023 H-21 Piasecki Curtiss The illuminating lamp is present

The illuminating lamp is present under the center top screw

This was a lighted instrument

But this is immediately noticeable

000 smooth contour

Helicopter Dual Tachometer Kollsman 981BX-8-023 H-21 Piasecki Curtiss The illuminating lamp is presentHere is a dual Tachometer for use in military helicopters, indicating RPM for the rotor on the inner scale and rotor for the outer scale with a ratio of 9. 7: 1. The pointers will be aligned once the rotors are fully engaged. It was used in the H 21 Shawnee Workhorse Piasecki Helicopter. There are some markings on the glass denoting the operating limits and orientation of the glass (the white mark, just in case it rotated). Measures 3. 25 inches