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Sundials were some of the first clocks in 800 BC. One of the earliest people to use the sundials were the Sumerians.These clocks depend on weather.
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Water clocks were needed to track night hours in 250 BC. They are formed by a bucket of water with a hole in the bottom, which water seeped through slowly. It wasn't the best of telling time though because it didn't keep exact hours. It also depended on weather.
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An hourglass is basically two bubbles of glass with a narrow middle used in the 14th century. Sand seeps through in a specified measure of time. This is the first clock that didn't depend on the weather.
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Grandfather clocks were big clocks that nhad weights and they would go up and down and back and forth to move gears and tell time. This is different from the hourglass because it is mechanical, and had moving parts.
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Although there are still many mechanical clocks, the most modern clocks are electronicand use digital technology to tell time.
