วันศุกร์ที่ 6 กรกฎาคม พ.ศ. 2555

Digital watch

A digital display simply shows the time as a number, e.g.12:08 instead of a short hand pointing towards the number 12 and a long hand 8/60 of the way round the dial. The digits are usually shown as a seven-segment display.
The first digital mechanical pocket watches appeared in late 19th century. In the 1920s the first digital mechanical wristwatches appeared.
The first digital electronic watch, a Pulsar LED prototype in 1970, was developed jointly by Hamilton Watch Company and Electro-Data, founded byPeter Petroff. John Bergey, the head of Hamilton's Pulsar division, said that he was inspired to make a digital timepiece by the then-futuristic digital clock that Hamilton themselves made for the 1968 science fiction film 2001: A Space Odyssey. On April 4, 1972, the Pulsar was finally ready, made in 18-carat gold and sold for $2,100. It had a red light-emitting diode (LED) display.
Digital LED watches were very expensive and out of reach to the common consumer until 1975, when Texas Instruments started to mass produce LED watches inside a plastic case. These watches, which first retailed for only $20, reduced to $10 in 1976, saw Pulsar lose $6 million and the Pulsar brand sold to Seiko.
An early LED watch that was rather problematic was The Black Watch made and sold by British company Sinclair Research in 1975. This was only sold for a few years, as production problems and returned (faulty) product forced the company to cease production.
Most watches with LED displays required that the user press a button to see the time displayed for a few seconds, because LEDs used so much power that they could not be kept operating continuously. Usually the LED display color would be red. Watches with LED displays were popular for a few years, but soon the LED displays were superseded by liquid crystal displays (LCDs), which used less battery power and were much more convenient in use, with the display always visible and no need to push a button before seeing the time. Only in darkness you had to press a button to lit the display with a tiny light bulb, later illuminating LEDs. The first LCD watch with a six-digit LCD was the 1973 Seiko 06LC, although various forms of early LCD watches with a four-digit display were marketed as early as 1972 including the 1972 Gruen Teletime LCD Watch, and the Cox Electronic Systems Quarza. In Switzerland, Ebauches Electronic SA presented a prototype eight-digit LCD wristwatch showing time and date at the MUBA Fair, Basle, in March 1973, using a Twisted Nematic LCD manufactured by Brown, Boveri & Cie, Switzerland, which became the supplier of LCDs to Casio for theCASIOTRON watch in 1974.
From the 1980s onward, digital watch technology vastly improved. In 1982 Seiko produced a watch with a small television screen built in, and Casio produced a digital watch with a thermometer as well as another that could translate 1,500 Japanese words into English. In 1985, Casio produced the CFX-400 scientific calculator watch. In 1987 Casio produced a watch that could dial your telephone number and Citizen revealed one that would react to your voice. In 1995 Timex released a watch which allowed the wearer to download and store data from a computer to their wrist. Some watches, such as theTimex Datalink USB, feature dot matrix displays. Since their apex during the late 1980s to mid 1990s high technology fad, digital watches have mostly become simpler, less expensive time pieces with little variety between models.
Despite these many advances, almost all watches with digital displays are used as timekeeping watches. Expensive watches for collectors rarely have digital displays since there is little demand for them. Less craftsmanship is required to make a digital watch face and most collectors find that analog dials (especially with complications) vary in quality more than digital dials due to the details and finishing of the parts that make up the dial (thus making the differences between a cheap and expensive watch more evident).

Analog watch


Traditionally, watches have displayed the time in analog form, with a numbered dial upon which are mounted at least a rotating hour hand and a longer, rotating minute hand. Many watches also incorporate a third hand that shows the current second of the current minute. Watches powered by quartz usually have a second hand that snaps every second to the next marker. Watches powered by a mechanical movement appears to have a gliding second hand, although it is actually not gliding; the hand merely moves in smaller steps, typically 1/5 of a second, corresponding to the beat (half period) of the balance wheel. In some escapements (for example the duplex escapement), the hand advances every two beats (full period) of the balance wheel, typically 1/2 second in those watches, or even every four beats (two periods, 1 second), in the double duplex escapement. A truly gliding second hand is achieved with the tri-synchro regulator of Spring Drive watches. All of the hands are normally mechanical, physically rotating on the dial, although a few watches have been produced with "hands" that are simulated by a liquid-crystal display.
Analog display of the time is nearly universal in watches sold as jewelry or collectibles, and in these watches, the range of different styles of hands, numbers, and other aspects of the analog dial is very broad. In watches sold for timekeeping, analog display remains very popular, as many people find it easier to read than digital display; but in timekeeping watches the emphasis is on clarity and accurate reading of the time under all conditions (clearly marked digits, easily visible hands, large watch faces, etc.). They are specifically designed for the left wrist with the stem (the knob used for changing the time) on the right side of the watch; this makes it easy to change the time without removing the watch from the wrist. This is the case if one is right-handed and the watch is worn on the left wrist (as is traditionally done). If one is left-handed and wears the watch on the right wrist, one has to remove the watch from the wrist to reset the time or to wind the watch.
Analog watches as well as clocks are often marketed showing a display time of approximately 10:09 or 10:10. This creates a visually pleasing smile-like face on upper half of the watch, in addition to enclosing the manufacturer's name. Digital displays often show a time of 12:08, where the increases in the numbers from left to right culminating in the fully lit numerical display of the 8 also gives a positive feeling.
Analog watch displays can be used to indicate cardinal direction due to the relation between the position of the hour hand and the position of the Sun in the sky. By rotating the watch so that the hour hand points toward the Sun, the point halfway between the hour hand and 12 o'clock will indicate south when observing from a position in the Northern hemisphere. In the Southern hemisphere, the point halfway between the hour hand pointed at the sun and 12 o'clock on the dial indicates North.
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