In 1933 , rolex invented the first wristwatch self - winding system with a free rotor , called the perpetual rotor , the precursor of contemporary self - winding systems . this innovation consists of a weight oscillating freely on a central axle . the watch is wound continuously thanks to wrist movements alone . the perpetual rotor provides the watch with a constant and stable source of energy maintaining its precision and enhancing comfort for the wearer , who in freed from the daily constraint of winding the watch .