Watch

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

Present watches are often digital watches, using a piezoelectric crystal, regularly quartz, as an oscillator.

In earlier times mechanical timepieces were used, motorized by a spring wound regularly by the user. The discovery of "Automatic" or "Self-Winding" watches allowed for a stable winding without particular action from the wearer: it works by an eccentric weight, called a winding rotor, which 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.


Types of watch

Pocket clock
The first necessity for portability in time keeping was steering 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 time zones; by comparing the noontime time of the local longitude to a European meridian, a sailor could know how far he was from home. However, the process was notoriously defective until the introduction of John Harrison's chronometer. For that reason, most maps from the 15th century to c.1800 have precise latitudes but indistinct longitudes.

The first reasonably exact mechanical clocks measured time with weighted pendulums, which are useless at sea or in watches. The creation of a spring mechanism was crucial for portable clocks. In Tudor England, the development of "pocket-clocks" 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 Heinlein created the first pocket watch. It is supposed that Henry VIII 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 bearing in mind the inexactness of the watch mechanism. Eventually, miniaturization of these spring-based designs allowed for exact portable timepieces which worked well even at sea. Aaron Lufkin Dennison founded Waltham Watch Company in 1850, which was the pioneer of the industrial developed by interchangeable parts, the American System of Watch Manufacturing.