page_title: History of timekeeping devices
section_title: Era of precision timekeeping
hierarchical_section_title: History of timekeeping devices / Era of precision timekeeping
context_page_description: For thousands of years, devices have been used to measure and keep track of time. The current sexagesimal system of time measurement dates to approximately 2000 BC from the Sumerians.
  The Egyptians divided the day into two 12-hour periods, and used large obelisks to track the movement of the sun. They also developed water clocks, which were probably first used in the Precinct of Amun-Re, and later outside Egypt as well; they were employed frequently by Persians and the Ancient Greeks, who called them clepsydrae. The Zhou dynasty is believed to have used the outflow water clock around the same time, devices which were introduced from Mesopotamia as early as 2000 BC.
  Other ancient timekeeping devices include the candle clock, used in ancient China, ancient Japan, England and Mesopotamia; the timestick, widely used in Persia, India and Tibet, as well as some parts of Europe; and the hourglass, which functioned similarly to a water clock. The sundial, another early clock, relies on shadows to provide a good estimate of the hour on a sunny day. It is not so useful in cloudy weather or at night and requires recalibration as the seasons change.
caption: The Dutch polymath and horologist Christiaan Huygens, the originator of the era of precision timekeeping,[128][129] was "the most ingenious watchmaker of all time" (in Arnold Sommerfeld's own words).[130]
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