Ryan Nagelhout 
Problem with Early Clocks [PDF ebook] 

Telling time wasn’t always as easy as looking at a cell phone. Clocks are incredibly complex machines that help make sure we’re on time for school and many other tasks in our everyday lives. But how did we learn how to tell time? What amazing minds learned how to make machines that helped us keep track of the days, hours, and minutes? From the early time-telling methods of Egyptian sun clocks and ancient Greek water clocks to the earliest watchmakers and today’s super accurate atomic clicks, telling time has been one of the many amazing things humans have learned to do.