Being able to look at a clock and check the time is something we all take for granted, but life would be a lot more complicated without accurate timing devices. This site, from Britannica.com, looks at ten manmade instruments that various civilizations have used to measure time. These clocks span many centuries, from the sundial in 1500 BC to the state of the art Cesium atomic clock. Some of the items come readily to mind, like the quartz watch, but others are much more obscure. For instance, not many people know how a clepsydra works. Both the physical operation of the devices and their historical significance are described in individual articles.