Disk Speed Indicator Mk XV for use with Norden Sight Grumman Nakajima J1N Bomber Gekko aka

Nakajima J1N Bomber Gekko aka "Irving"

The measuring triangle was used to optimize the fire efficiency of machine guns and to calculate distances

is presumed to be WW II era from an aircraft of the Armée de l'Air

Measures 5 inches by 5 inches by 8 inches long

Disk Speed Indicator Mk XV for use with Norden Sight Grumman Nakajima J1N Bomber Gekko akaThe Disk Speed Indicator Mk XV was used by WWII US Army Air Force and Navy bombardiers to verify and calibrate the disk speed of the Norden Bomb Sight during flight before initiating the bomb run. The disk speed is the parameter which determined the duration of flight between sighting of the target and automatic release of the aircraft's ordnance. With the bomb sight switched on, the bombardier would affix the top axle to the small female receptacle