printed-circuit card, to reset the timing circuit. When the armature picks up it also raises the driving spring enough to clear the next tooth on the ratchet wheel and the driving spring snaps into the next notch. When the SCR is turned off by the SA contact, the armature coil is de-energized and its main spring rotates the ratchet wheel 10°. At this point the timer starts timing again, and it will rotate the stepping-switch ratchet wheel another 10° after another time interval has elapsed. All stepping-switch operations will have the same time interval.