For thousands of years different from, calendars and other technical means used to carry out the Christian era, that is, measuring the time interval or determine the current astronomical time. Early examples of applications was to predict the dark, to plan the sowing and harvesting, to remember the celebrations and to navigate .
The current sexagesimal dividing the time interval into 60 equal parts, invented by Sumerians and has been used for measurement of time of about 4 000 years. The ancient Egypt divided the day into two 12-hour periods, and used large obelisks to track the sun’s position. They also developed water clock , which probably first used in the Amun-Res temple complex of Karnak in Egypt and later in ancient Greece . The Greeks often used the Egyptian water clock, which they called klepsydra. The Chinese Shang Dynasty is believed to have used water-cut at about the same time, after the technology had come in through Mesopotamia as early as 2000 BC . The Chinese were also the first to divide the day into 100 equal intervals, as in 2000 it represented a short quarter (= 14.4 minutes ). Other antique timepieces were light clock , used in China, Japan, England and Iraq, the time gauge, a kind of portable sundial that was widely used in India, Tibet, and in some parts of Europe as well as various types of hourglass , which in principle is as water clocks.
As first mechanical timepiece, the earliest clocks used the sun’s shadows and was therefore not put to use at night or in cloudy weather. They also needed to be recalibrated according to season, except in the cases solurets gnomon was in line with the Earth’s axis . The earliest known water clock, with a water-driven balance system that converted the rotary motion to a range of motion, is dated to 200’s and was used in Greece. In China invented mercury-run movements in the 900s, followed by Arab water clock with gears and weights in the 1000’s.
Mechanical watches with step wheel was invented in Europe in the early 1300s and remained the most common urmekanismen until spring powered clocks and pocket watches were invented in the 1500s, followed by the pendulum clocks in the 1600s. In the 1900s developed the quartz oscillator and the atomic clock . Quartz oscillator, which initially mainly used in the laboratory context, was both accurate and could be manufactured at a reasonable cost and therefore became common in watches .
Atomic clocks are more accurate than any previous tidmätningsenhet and is used to calibrate the other bells and for calculating the international atomic time as the standardized civil system, UTC is based.