In an automatic watch, the movements of the rotor can be converted into mainspring twists either
- unidirectionally. Seen in the Miyota 8215, ETA 7750 and others. Simpler than bidirectional, but wastes half of the energy present and may cause the rotor to spin noisily in the idle direction.
- bidirectionally, either via reversers or pawls like the Magic Lever system. Rolex 3135 uses reversers, as do most ETA movements. Most Seiko uses magic lever, the rest vary but in Swiss movements reversers are dominant.
There are also more exotic variations like the IWC Pellaton system.