Today, surrounded as we are by clocks and watches, it is hard to imagine life without an exact method of timekeeping. Until the mechanical clock was invented and improved, people had a less precise sense of the passage of time, based largely on the movement of the sun across the sky and measured with sundials, sandglasses, and other simple devices. It wasn't until the eighteenth century that John Harrison invented a truly reliable clock. Harrison's final invention, H-4, was the first accurate and portable mainspring clock. Meanwhile, stationary timekeepers such as longcase (or grandfather) clocks, table clocks, and large public clocks had become accurate to within seconds, allowing people to structure their lives according to the exact minute. Electric, quartz, and atomic clocks and watches have since allowed ever more perfect timekeeping. Turning Point Inventions is the first series of books to focus on the important inventions we often take for granted and how they have affected our lives. In lively text and fascinating pictures, these books explore the world before the invention; the life of the inventor and how he or she came upon the discovery; how the world was changed by the invention; and how it may influence our future. A special full-color foldout in each book shows in detail how the invention works.