The "Magic lever" is a characteristic element found in many SEIKO mechanical watches. This mechanism is used for auto-winding of the mainspring.
The back and forth motion of the magic lever forces a ratchet gear to rotate in one direction only. That gear rewinds the mainspring which is enclosed in the barrel.

*(See the [original video](https://youtu.be/eN0uNhS3Vrg) on Seiko's YouTube channel.)*
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The Magic Lever can also be found in the TAG Heuer [Calibre 1887](https://www.tagheuer.com/en/calibre-1887).
