Ammunition Reserve Counter, B-36 Peacemaker

This is a US Air Force, Cold-War-era 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 used to reset the counter to zero once pressed, but it is either non-functional or requires the correct electrical input to function.  

Two of these counters were installed in the tail gunner's position on the Convair B-36 Peacemaker bomber (see illustration from the B-36 Flight Manual). It may also have been used in other Cold-War-era aircraft of the US Air Force. Measures ~2 inches wide by ~2.5 inches high and deep.  It is in good cosmetic condition.