Helicopter Dual Tachometer Kollsman 981BX-8-023 H-21 Piasecki Curtiss This was a lighted instrument

This was a lighted instrument

There is a thin sliding ring around the dial to which a small triangular pointer is attached

But this is immediately noticeable

with BU AERO US NAVY on its data label

made by Fairchild

Helicopter Dual Tachometer Kollsman 981BX-8-023 H-21 Piasecki Curtiss This was a lighted instrumentHere 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