Bidirectional winding is a self-winding system in which the rotor produces energy whichever way the wearer’s movement swings it. It usually builds up energy faster than a rotor that winds one way only. It is not twice as efficient, though, because no energy is produced while the rotor changes direction.
How does bidirectional winding work?
The rotor swings back and forth with the wearer’s movement. The movement has to turn that motion, in either direction, into power for winding the mainspring. In the ETA automatic movement, a pair of click-wheels does this job. Each click-wheel has an upper and a lower half. One-way ratchets lock or free these halves depending on which way the rotor turns. Other self-winding designs use two ratchets for the same purpose. Either way, the oscillating weight winds the mainspring whether it swings clockwise or anticlockwise.
What is Seiko’s Magic Lever?
Seiko developed the Magic Lever in 1959. It is a small, scissor-shaped part for self-winding watches. Whichever way the rotor turns, the lever moves up or down. That motion lets the rotor wind in both directions without a pair of click-wheels. The result is the same as in a click-wheel system: the rotor winds in both directions. The part that makes it happen is different.
Not to be confused with
Unidirectional winding works differently. The rotor stores energy only when it turns one way and produces none when it turns the other. Over the history of self-winding watches, some designs used bidirectional winding and others used unidirectional winding. NOMOS Glashütte says its bidirectional rotors have a large radius and a reverse angle of only 10 degrees.
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