The first self-winding Rolex wristwatch was offered to the public in 1931 (so-called the “bubbleback” due to the large caseback), preceded to the market by Harwood which patented the design in 1923 and produced the first self-winding watch in 1928, powered by an internal mechanism that used the movement of the wearer’s arm. This not only made watch-winding unnecessary, but kept the power from the mainspring more consistent resulting in more reliable time keeping.

-Wikipedia

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