Martin Burgess Clock B is based on John Harrison 's 18th century design . Clock was strapped to a pillar at the Royal Observatory in Greenwich . The clock has been restored and now runs 24 hours a day, with an automatic wind up mechanism that can be set by hand or by computer. Certified by Guinness Book of Records , National Maritime Museum said .
Martin Burgess Clock B is based on John Harrison 's 18th century design . Clock was strapped to a pillar at the Royal Observatory in Greenwich . Time measured using a radio-controlled clock and the BT speaking clock . Certified by Guinness Book of Records , National Maritime Museum said .