Rolex 'Oyster Perpetual' wristwatch, 1931.

The Rolex Oyster Perpetual rotor self-winding wristwatch, introduced in 1931, incorporated a self-winding mechanism which became the standard form for all subsequent automatic wristwatches. The Perpetual movement transforms each movement of the wrist into a reserve of power which keeps the mainspring at optimum tension, thereby ensuring greater accuracy and reliability.