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A watch is a small timepiece intended to be carried or worn by a person. It is designed to keep working despite the motions caused by the person's activities. A wristwatch is designed to be worn on a wrist, attached by a watch strap or other type of bracelet. A pocket watch is designed for a person to carry in a pocket. Watches evolved in the 17th century from spring-powered clocks, which appeared as early as the 14th century. The first watches were strictly mechanical, driven by clockwork. As technology progressed, mechanical devices, used to control the speed of the watch, were largely superseded by vibrating quartz crystals that produce accurately timed electronic pulses. Some watches use radio clock technology to regularly correct the time. The first digital electronic watch was developed in 1970.〔Pulsar LED (Smithsonian )〕 Most inexpensive and medium-priced watches, used mainly for timekeeping, are electronic watches with quartz movements.〔 Expensive collectible watches, valued more for their elaborate craftsmanship, aesthetic appeal and glamorous design than for simple timekeeping, often have purely mechanical movements and are powered by springs, even though these movements are generally less accurate and more expensive than electronic ones. Various extra features, called "complications", such as moon-phase displays and the different types of tourbillon, are sometimes included.〔Wikipedia: sections under Functions.〕 Modern watches often display the day, date, month and year, and electronic watches may have many other functions. Time-related features such as timers, chronographs and alarm functions are common. Some modern designs incorporate calculators, GPS〔(【引用サイトリンク】url=http://www.theverge.com/2012/2/21/2814819/epson-world-lightest-gps-watch-japan )〕 and Bluetooth technology or have heart-rate monitoring capabilities. Watches incorporating GPS receivers use them not only to determine their position. They also receive and use time signals from the satellites, which make them essentially perfectly accurate timekeepers, even over long periods of time. Recent developments include smartwatches, which are elaborate computer-like electronic devices designed to be worn on a wrist. They generally incorporate timekeeping functions, but these are only small fractions of what the watch can do. The study of timekeeping is known as horology. ==History== (詳細はspring-driven clocks, which first appeared in 15th century Europe. Watches weren't widely worn in pockets until the 17th century. One account says that the word "watch" came from the Old English word ''woecce'' which meant "watchman", because it was used by town watchmen to keep track of their shifts at work. Another says that the term came from 17th century sailors, who used the new mechanisms to time the length of their shipboard ''watches'' (duty shifts). A great leap forward in accuracy occurred in 1657 with the addition of the balance spring to the balance wheel, an invention disputed both at the time and ever since between Robert Hooke and Christiaan Huygens. This innovation increased watches' accuracy enormously, reducing error from perhaps several hours per day〔Milham 1945, p.226〕 to perhaps 10 minutes per day, resulting in the addition of the minute hand to the face from around 1680 in Britain and 1700 in France. The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two century wave of watchmaking innovation. The first thing to be improved was the escapement. The verge escapement was replaced in quality watches by the cylinder escapement, invented by Thomas Tompion in 1695 and further developed by George Graham in the 1720s. Improvements in manufacturing such as the tooth-cutting machine devised by Robert Hooke allowed some increase in the volume of watch production, although finishing and assembling was still done by hand until well into the 19th century. A major cause of error in balance wheel timepieces, caused by changes in elasticity of the balance spring from temperature changes, was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw. The lever escapement was the single most important technological breakthrough, and was invented by Thomas Mudge in 1759 and improved by Josiah Emery in 1785, although it only gradually came into use from about 1800 onwards, chiefly in Britain. The British had predominated in watch manufacture for much of the 17th and 18th centuries, but maintained a system of production that was geared towards high quality products for the elite. Although there was an attempt to modernise clock manufacture with mass production techniques and the application of duplicating tools and machinery by the British Watch Company in 1843, it was in the United States that this system took off. Aaron Lufkin Dennison started a factory in 1851 in Massachusetts that used interchangeable parts, and by 1861 it was running a successful enterprise incorporated as the Waltham Watch Company.〔. Reprinted by McGraw-Hill, New York and London, 1926 (); and by Lindsay Publications, Inc., Bradley, Illinois, (ISBN 978-0-917914-73-7).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「watch」の詳細全文を読む スポンサード リンク
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