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Egyptians could tell time by the shadow thrown by the sun on an unmoving subject. They used an obelisk. That is a verticale construction with four sides, as a shadow clock, placing it in the sun so that it could throw a shadow.
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People in Babylonia used a sundial, which a flat circle on which a 12-hour clock face, or dial, was written. They also attached a gnomon (=vertical marker) to the middle of the dial.
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The Europeans used the hourglass at any time, which was one of the first timekeepers. These timekeepers (or timepieces) are tools designed for telling time without using the sun.
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The first mechanical clocks appeared in Europe
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The first watches showed up in Italy. These timepieces could be weared or carried.
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European scientists and inventors found at that this world would make the clock much better in setting time precisely. The pendulum is a rod-like weight that swings from side to side and it controls a clock mechanism.
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GMT = Greenwich Mean Time; time measured in each time zone. It is 1 hour later than in time zone West. It is 1 hour earlier than in time zone East.
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UTC = Universal Time Coordinate; this new very exact system, was approved over the whole world as the official measure of time for the planet.