On the evening of 13th March 2008, between the hours of 6:00pm and 2:00am, five reflection holograms were recorded of John Harrison’s fourth timekeeper ‘H4’, at the Royal Observatory, National Maritime Museum in Greenwich, London. Arguably the most important timekeeper ever made this watch finally solved one of the greatest scientific problems of its time, that of finding Longitude and marked the beginning of accurate global positioning. In recent years public awareness of the watch has witnessed an unprecedented level of popularity, together with a string of authoritative writings including the release of Dava Sobels book, ‘Longitude’, with introduction by NASA astronaut Neil Armstrong, a filmed drama adaptation and even a television sitcom ‘Only Fools and Horses’ where viewing figures reached a record twenty–four million. The watch, its history and its place in history, remain subject of fascination and curiosity. Now its journey to hologram is traced in this paper through the events of that March evening.
