OM 5 Science has us learning about astronomy. In our study of early, practical applications of astronomy by the Egyptians, we learned about sundials. One assignment required Thing 3 to make a sundial and try to tell time with it, checking himself against a clock. It was difficult at first, but he got pretty good at it fairly quickly.
We made this very simple yet effective sundial by placing a pencil in a ball of clay. Every hour, Thing 3 went out and marked the hour with a stone. This sundial goes from 9 a.m. to 4 p.m. Easy cheesy! And fun!