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Early Egyptians told time by the shadow cast by the sun on an stationary object, the obelisk.
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The early Greeks and Egyptians designed a water clock. It used the flow of water to measure time. The water reaching certain lines drawn on the container showed that a certain amount of time had passed.
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In ancient China, people tied knots at regular intervals on a rope and burned it to show passage of time.
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People used notches in candles to represent periods of time. How much time passed depended on how many notches had been burned since the candle was lit.
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By 300 BCS, the Babylonians started using a sundial with a 12-hour clock face.
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By the 11th century, Europeans used the hourglass, which could be used day or night.
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These clocks used physics principles of weights and balances to mark out increments of time over a 12-hour period. Unfortunately, they weren't very accurate yet.
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Timepieces that people could wear or carry appeared in Italy. They measured time through a system of coiled springs.
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Scientists and inventors in Europe discovered the adding a pendulum greatly increased a clock's accuracy and preciseness. It could also now record minutes and seconds as well as hours.
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Standard time was a way for people from all over the world to standardize to meet common needs. Standard time divides the earth from top to bottom into 24 equal time zones.
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The first digital clock was invented.
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The atomic clock is the most accurate time-keeping device invented so far. The materials have changed since it was first developed in the 1940s.
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This was a new, highly accurate system that was adopted around the world as the official measure of time for the planet.
