The is a Soviet Military Chronometer, Model AChS1.

This clock is fully mechanical, very accurate and works for 48 hours from one full spring wind.

The chronometer has some additional functions - built-in stopwatch (lower dial) and a flight duration timer (upper dial). The "Flight Time" dial has a small window with 3 indicators - red, white, and red/white. The initial position of this indicator can be set with the left crown.

The crowns are also multifunctional. You will have to play with them to see what they do (if you need mode details - please ask)

There are two electrical connectors on the back of the watch, I assume this is for a built-in heater, uses 27 VDC on-board power.

This model was used on several Soviet aircraft - MiG, SU and probably others.