A self-winding mechanism is a more technically complicated method of winding a watch than the typical hand winding one. It involves a rotor which is attached to a ratcheted winding mechanism and pivots on an axis and is activated by the movement of the wearers arm.
The arm movement causes the rotor to turn and and through a series of reverser and reducing gears, eventually winds the mainspring.
A self-winding watch is also commonly referred to as an automatic watch.
These days self-winding watches have two ratchets and wind the mainspring during clockwise and anticlockwise rotor motions.
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