Automatic Movement
A mechanical movement that winds its mainspring automatically through the motion of a rotor as the watch is worn.
Also known as: self-winding movement, automatic calibre, automatic caliber, self-winding watch
Definition
An automatic movement is a mechanical movement that winds its mainspring using motion from the wearer's wrist. A weighted rotor or oscillating mass rotates as the watch moves; a winding train converts that motion into rotation of the barrel arbor so the mainspring is replenished. Depending on the design, winding can occur in one or both rotor directions. A slipping bridle in many automatic barrels prevents damaging over-winding once the mainspring is fully tensioned. Most modern automatics can also be wound through the crown.
Why it matters
Automatic winding makes a mechanical watch convenient for daily wear because normal wrist movement can keep it running. Rotor design also affects movement thickness, visibility, winding efficiency and sometimes the feel or sound of the watch.