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History of timekeeping devices.
For thousands of years, devices have been used to measure and keep track
of time (timekeeping or timing). 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,
relles on shadows to provide a good estimate of the hour on a sunny day. It is
not so useful in cloudy wentho​