Automatic watches are mechanical wrist watches, in which the mainspring is wound up by a rotor through arm-movement of the user.
The mainly ball bearing mounted rotor will be more stationary when the watch is moved, through gravity and its mass inertia, so that a moment of force is exerted onto the winding up mechanism. Usually the mainspring will be wound up by movements in both directions (bi-directional). Through gyrating movement of the rotor, vertical to the axle, its own eccentricity comes into effect. The rotor is usually formed as a half circle, so that its centre of gravity doesn’t overlap with its own axle. If the watch is moved, even slightly over its horizontal axle, the rotor will perform a 180° turn. If the watch is fully wound up already, a so called bridge (a friction clutch) will prevent an over winding of the mainspring.
Automatik watches are mechanical watches with the spring being wound by a rotor, which rotates when the wearer moves his arm