A watch is a small portable clock that displays the current time and sometimes the current day, date, month and year. In modern times they are usually worn on the wrist with a watch-strap, although before the 20th century most were pocket watches, which had covers and were carried separately, often in a pocket, and hooked to a watch chain.

In earlier times mechanical timepieces were used, powered by a spring wound regularly by the user. The invention of "Automatic" or "Self-Winding" watches allowed for a constant winding without special action from the wearer: it works by an eccentric weight, called a winding rotor, that rotates to the movement of the wearer's body. The back-and-forth motion of the winding rotor couples to a rachet to automatically wind the watch.

Watches may be collectible; they are often made of precious metals, and can be considered an article of jewelry.

Types of watch

Pocket clock
The first necessit for portability in time keeping was navigation and mapping in the 15th century. The latitude could be measured by looking at the stars, but the only way a ship could measure its longitude was by comparing timezones; by comparing the midday time of the local longitude to a European meridian (usually Paris or Greenwich), a sailor could know how far he was from home. However, the process was notoriously unreliable until the introduction of John Harrison's chronometer. For that reason, most maps from the 15th century to c.1800 have precise latitudes but distorted longitudes.

The first reasonably accurate mechanical clocks measured time with weighted pendulums, which are useless at sea or in watches. The invention of a spring mechanism was crucial for portable clocks. In Tudor England, the development of "pocket-clockes" was enabled through the development of reliable springs and escapement mechanisms, which allowed clockmakers to compress a timekeeping device into a small, portable compartment. In 1524, Peter Henlein created the first pocket watch. It is rumoured that Henry VIII (the portrait of Henry VIII at this link shows the medallion thought to be the back of his watch) had a pocket clock which he kept on a chain around his neck. However, these watches only had an hour hand - a minute hand would have been useless considering the inaccuracy of the watch mechanism. Eventually, miniaturization of these spring-based designs allowed for accurate portable timepieces which worked well even at sea. Aaron Lufkin Dennison founded Waltham Watch Company in 1850, which was the pioneer of the industrial manufacturing by interchangeable parts, the American System of Watch Manufacturing.

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