In the mechanical design of practically all types of instruments, it is necessary for certain parts to operate intermittently relative to a continuously moving part. A popular and simple means of obtaining this movement is by the use of the Geneva mechanism. — The Geneva mechanism is so named because its operation is based upon the principle of the stop in Geneva watches which prevents overwinding the mainspring by checking the winding stem after a predetermined number of turns. Now universally used in motion picture projectors for synchronizing the movement of the film with that of the shutter, the Geneva mechanism also has various applications in indexing devices for machine tools. In the design of communications and navigational equipment, it is useful for electrical tuning and band change drives (see Fig. 1), in dial indicating mechanisms, in coil tuning and switch positioning, and in numerous other applications.