Description: The Seiko "4207" mechanism is designed for Ladies' watches. It measures about 17mm in diameter. It uses a ball bearing quarter-arc rotor and can be hand-wound.

The 4207 is a tiny movement which also uses an equally tiny main spring. Its power reserve is significantly smaller than the 7s caliber which has a bigger main spring. The smaller mass of the oscillating rotor may also mean that automatic winding is less efficient compared to the bigger mass of a typical 7s rotor. Therefore, it makes sense to add a manual wind feature to assist in keeping the main spring fully wound. The 4207 doesn't hack and thus cannot be synchronized to a time source. Seiko decided that this feature probably was not important for the target consumer.