Young Blonde Girl With A Wrist Watch Undresses Her Purple Shirt On The Rattan Furniture In The Backyard Garden

Traditional mechanical watch movements use a spiral spring called a mainspring as a power source. In manual watches the spring must be rewound periodically by the user by turning the watch crown. Antique pocketwatches were wound by inserting a separate key into a hole in the back of the watch and turning it. Most modern watches are designed to run 40 hours on a winding and thus must be wound daily, but some run for several days and a few have 192-hour mainsprings and are wound weekly.
• Automatic watches
A self-winding or automatic watch is one that rewinds the mainspring of a mechanical movement by the natural motions of the wearer's body. The first self-winding mechanism was invented for pocket watches in 1770 by Abraham-Louis Perrelet, but the first "self-winding", or "automatic", wristwatch was the invention of a British watch repairer named John Harwood in 1923. This type of watch allows for constant winding without special action from the wearer; it works by an eccentric weight, called a winding rotor, which rotates with the movement of the wearer's wrist. The back-and-forth motion of the winding rotor couples to a ratchet to automatically wind the mainspring. Self-winding watches usually can also be wound manually so they can be kept running when not worn or if the wearer's wrist motions are inadequate to keep the watch wound.