In ancient times people measured time by the movement of the stars, moon and sun. Then people began to use sundials to cast a shadow to tell the time, and even as long ago as 1500 BC the ancient Egyptians had portable ones. There were also water clocks or 'clepsydra' which measured the time water took to flow out of a vessel, hourglasses where sand flowed from one chamber into another, and candles which had markings on them to show how much time they had been burning.

The first mechanical clocks appeared around the 14th century and the first one that struck the hour was erected in Milan, Italy in 1335. In the 1600s Christiaan Huygens used the pendulum in clocks for regular movement and in 1670 the long pendulum in the Grandfather clock could record minutes as well as hours. In 1721 George Graham's pendulum clocks were so accurate that they lost no more than 1 second a day. These days there are many different types of clocks, from wind up mechanical to electric ones, and watches that are charged by kinetic energy from the movement of your wrist as you walk. The most accurate clock in the world is the Caesium Atomic clock.