Driving wheel 1 rotates about fixed axis A and its tooth a periodically engages a pin of driven pin wheel 2, rotating the pin wheel about fixed axis B through a certain angle. Thus, when wheel 1 rotates continuously, wheel 2 rotates intermittently with dwells. Wheel 2 is locked during its dwell periods by pawl 3 which turns about fixed axis C. Pawl 3 is brought into and held in engagement with pin wheel 2 by concentric cam surface b-b of wheel 1.
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