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 the Guinness World Records 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 .