5 About 700 years ago, people started to make mechanical clocks. At first, they used weights to power these clocks. The clocks told the hour with bells. However, the weights were big and heavy, so these clocks were difficult to move. 5 6 About 500 years ago, people improved tbaur clocks. They used springs to power the clocks.se springs were small and light. So people could move っる the clocks easily. Eventually, people began to carry watches. [74 words] 10