This review is top notch and comprehensive. It's the book of choice to cover the background and the technology. I'm not a watch or clock fanatic, but I slam dunked this whole book in just a couple days; a 15 hour Qantas flight kept me captive. I wish there was more discussion on the nature of astronomy and how the clocks were calibrated. I want to read up on octants, sextants and basic navigation now. This book deserves five stars. The A&E four hour documentary, "Longitude", this month also deserves high marks. If someone knows of a good read on navigating with astronomy that's more layman oriented, please email me (thanks).