In 1931, Rolex invented the world’s first self-winding mechanism with a perpetual rotor. On the front of every automatic Rolex watch, you will find the words, “OYSTER PERPETUAL,” just below “ROLEX” on the front of the dial. These terms refer to the self-winding mechanism housed inside of the Rolex case. The term “self-winding” means that the watch is wound by the natural movement of the wearer’s arm and never needs to be manually wound. However, each Rolex does have a crown that allows the wearer to wind it manually. This mechanism consists of a half moon-shaped oscillating weight. It pivots freely in one direction and transmits uninterrupted natural energy to the watch, which is then stored in the mainspring. According to Rolex, “the Perpetual rotor system of the Oyster movements is recognizable by two red reversing wheels that allow the rewinding of the movement regardless of the rotation direction of the oscillating weight. Most automatic movements have jewels on the movement, which reduce friction between the moving parts in the watch." In most cases, the number of the jewels will be engraved on the movement. In 1923, John Harwood invented the first self-winding wristwatch, which was called the 'Bumper' wristwatch. In 1930, Rolex perfected the design, using it as the basis for its Oyster Perpetual movement. One of the main differences between the Rolex movement and the movement from the “Bumper” wristwatch was that the Rolex movement could rotate a full 360 degrees, where the 'Bumper' movement only rotated 300 degrees. This extra rotation allowed Rolex’s version to store more energy in the mainspring and run independently for up to 35 hours.
The term “caliber” refers to the movement, or the internal mechanism, of a watch. Each movement has a reference number that is found on the case at 12 o’clock. Rolex first and foremost concern has always been to create quality movements that were precise and accurate. In 1910, a Rolex watch received the Swiss Certificate of Chronometric Precision, making it the first wristwatch in the world to receive this honor. In 1910, a Rolex watch was awarded a class “A” precision certificate, which, until then, had only ever been granted to marine chronometers. Since the company’s inception, Rolex has been known for its accurate and precise watches.