An optical device to make an indicator diagram for high-speed engines. It is made of a light-tight package or digital camera having at one end a little convex mirror which reflects a beam of light onto the ground glass or photographic plate on various other end. The mirror is pivoted so that it is moved in one course by a tiny plunger operated by an elastic metal diaphragm which closes a tube related to the motor cylinder. Additionally it is moved at correct angles to the path by a reducing motion, labeled as a reproducer, to be able to duplicate accurately on a smaller sized scale the movement of this motor piston. The resultant of those two moves imparts towards reflected laser beam a motion similar to that of the pen for the ordinary signal, and this can be tracked on the sheet of floor glass, or photographed.
a computer device for which a beam of light, going over a ground-glass screen, shows the stress in cylinder at any point associated with swing for confirmed motor: applied to high-speed machines, at the time of motor-cars, that are too small for ordinary indicators.