This is a comprehensive, illustrated catalogue of the 200+ marine chronometers in the collections of Royal Museums Greenwich. Every chronometer has been completely dismantled, studied and recorded, and illustrations include especially commissioned line drawings as well as photographs. The collection is also used to illustrate a newly researched and up-to-date chapter describing the history of the marine chronometer, so the book is much more than simply a catalogue. The history chapter naturally includes the story of John Harrison’s pioneering work in creating the first practical marine timekeepers, all four of which are included in the catalogue, newly photographed and described in minute detail for the first time. In fact full technical and historical data are provided for all of the marine chronometers in the collection, to an extent never before attempted, including biographical details of every maker represented. A chapter describes how the 19th century English chronometer was manufactured, and another provides comprehensive and logically arranged information on how to assess and date a given marine chronometer, something collectors and dealers find particularly difficult. For further help in identification of chronometers, appendices include a pictorial record of the number punches used by specific makers to number their movements, and the maker’s punches used by the rough movement makers. There is also a close-up pictorial guide to the various compensation balances used in chronometers in the collection, a technical Glossary of terms used in the catalogue text and a concordance of the various inventory numbers used in the collection over the years.