There are excellent books discussing time at a level accessible for the general reader (e.g. Empires of Time, by Anthony Aveni). The Quantum Beat is the only one I've seen that gives a thorough discussion of the basics and then goes on to give an incredibly lucid discussion of all the minute details involved in making more and more accurate clocks. He elaborates on the pluses and minuses of each new development, from the sundial to the pendulum clock to the quartz crystal clock to the atomic clock. He also outlines the directions currently being pursued -- clocks based on a single atom held in an atom trap. The book will have special appeal to those who know about physics, crystals or engineering, and it should make fascinating reading for any educated layperson. Major was a key figure in the development of atomic clocks and has produced an exhilarating book describing their importance and the incredible technological efforts that went into their development.