Ammunition Reserve Counter

This is an electromechanical Ammunition Reserve Counter, used to display the rounds of ammunition remaining in reserve, up to 999 rounds, as the aircraft's guns have been fired. The wheel at the left of the digit display counter is used to set the total rounds loaded into the aircraft.  The small protrusion right of the digit display counter was likely used to reset the counter to zero once pressed, but it is either non-functional or requires the correct electrical input to function.  

We are speculating that this is from a fighter aircraft of the 1950s or 1960s. Measures ~2 inches wide by ~2.5 inches high and deep.  It is in good cosmetic condition.