Tachometer, Helicopter, USSR 0-4000 RPM C-7 The Suction Gage measured the

The Suction Gage measured the amount of vacuum generated to power the pneumatically-operated gyroscopic instruments

The glass is clear and intact

For example

Doing so rotates the circular inset card displaying the BHP

such as the P-40

Tachometer, Helicopter, USSR 0-4000 RPM C-7 The Suction Gage measured theHere is a Cold War era electronic dual Tachometer, 0 4000 RPM, as used in military helicopters of the USSR and Poland such as the MIL MI 1 (see cockpit photo, the tachometer is in the middle of the second column of instruments from the right) and MIL MI 4 (see cockpit photo, the tach is in the bottom row 3rd instrument from left). The pointer labeled "P" indicates RPMs of the Rotor, while the pointer labeled "M" indicates RPMs of the Engine. It is in