Telling Time Through the Ages Author:Rebecca Weber Approximately 5,000 to 6,000 years ago, people began to make clocks: tools that can precisely mark off equal lengths of time. In this book, you will find out about several types of clocks invented throughout history. You will also discover that you can make some of these clocks yourself by following step-by-step instructions. You will even measu... more »re your body clock!« less