I'm not sure if this info has already been posted. I'll leave it up to the moderator to pull the thread if it has. This is a brief description of the machine used by Leitz to check their shutters back in 1946. From the British Intelligence survey of the Leitz factory in 1946. The timing of the fast range of the shutter is carried out with the aid of a stroboscope of somewhat antique design. By means of this the 1/200, 1/500 and the 1/1000 speeds are checked. The stroboscope consists of a revolving drum placed horizontally, with 33 horizontal slits in its surface, illuminated from inside by a lamp of approximately 20 watts. The drum is driven by a belt from an electric motor which may be controlled by a rheostat. The drum is also coupled to a speedometer in order that its speed may be set. The correct speed for the drum to rotate at was 280 r.p.m. The camera is held on a wooden block in such a manner that the light from the rotating drum falls on the blinds of the focalplane shutter. The shutter is then fired and a series of stroboscopic lines are seen in the aperture. If the shutter is correctly set these lines appear vertically but if the shutter is incorrectly set the lines will curl down either to the left or to the right according to whether the shutter is set too slow or too fast. The checking of the lower speeds was only carried out on the 1/20 second and 1/4 second settings by means of a revolving series of lights. The various speeds of the shutter were not accurate to the measurements on the shutter control knob and this fact was acknowledged by the Leitz executives. who pointed out, however, that the results obtained were quite good enough for all general requirements. A metronome was used in checking the one second escapement.