Disk Speed Indicator Mk XV for use with Norden Sight Grumman See instruction page from the

See instruction page from the SCR-595 manual in the photo gallery

Type D-1 (also AN5816-2)

the soldiers and officers of the Armed Forces of the Committee for the Liberation of the Peoples of Russia

Six mounted in in various places

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

Disk Speed Indicator Mk XV for use with Norden Sight Grumman See instruction page from theThe 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