Automatic speed/time recorder utilising the principle of the stroboscope

This letter contains a description of the mode of operation of an automatic rotational speed/time recorder based on the principle of the stroboscope. The device produces a record of speed against time, on punched paper tape, for a rotating electrical machine during the progress of a retardation test. The data output on the punched tape represents the time taken for the machine speed to fall by successive equal decrements.