For thousands of years, clocks have been used to measure and track the passage of time. The 60-decimal unit of time in use today was conceived in Sumer in about 2000 B.C. It was the ancient Egyptians who divided the day into two sets of 12 hours, with the shadow of a giant obelisk as a sundial. They also made a water clock, which was probably first used near Luxor Water clocks were later used outside of Egypt as well. In ancient China, water clocks were invented using a system of overflowing water, and this water clock technology is thought to have come from Mesopotamia around 2000 BC. Other candle clocks were also used in China, Japan, England, and Iraq, and sundials were widely used in India, Tibet, and parts of Europe.
The first to use escapement (a device to turn gears in a certain direction) in clocks was in China in the 8th century, and it was the Muslims in the 11th century who incorporated gears and weights into water clocks; the first to use verge escapement for escapement was in Europe in the 14th century and in the 16th century It was used for a long time until the spring-loaded pocket watch and the pendulum clock in the 18th century, before being replaced by quartz and then atomic clocks in the 20th century.
