Disk Speed Indicator Mk XV for use with Norden Sight Grumman is presumed to be WW

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

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

and likely used in other bombers such as the Vickers Wellington and Short Stirling

The outer rim has been painted red and white to denote a preferred operating range

Disk Speed Indicator Mk XV for use with Norden Sight Grumman is presumed to be WWThe 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