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The water clock dates back to 16th century B.C. Babylon and was used by the Greeks. It is one of the earliest forms of timekeeping devices that uses a steady flow of water to track time. With this device, a large bowl would be filled with water and allowed to slowly drain from a spout at the bottom. The inside of the bowl was marked with time intervals. This enabled them to determine how much time had passed by the water level in the bowl. Water clocks were largely used to determine the hours of nighttime.