In “A Description Concerning Such Mechanism as will afford a nice, or True Mensuration of Time…” written in 1775, one year before his death, John Harrison penned the claim that the application of his science to horology would produce a clock capable of remaining within one second in 100 days. As Harrison did not complete his last clock (now known as the RAS regulator) his claim remained unproven and the subject of much ridicule. Two hundred years later, clockmaker Martin Burgess began the construction of two clocks of his own unique design that would apply Harrison’s theory without replicating Harrison’s clock. Both the “Gurney Clock”, a commissioned work known as “Burgess Clock A”, and “Burgess Clock B” were begun in 1974, with Clock A completed in 1984 and delivered to Norwich before the adjustments were complete. Clock B remained incomplete for over 30 years when, with guidance from William Andrewes, Andrew King and Donald Saff, Frodsham & Co., under the direction of Philip Whyte and Richard Stenning, was commissioned in 2009 to complete the clock in consultation with Mr. Burgess, Mervyn Hobden, and others from the distinguished cadre of horologists known as the Harrison Research Group. Roger Stevenson and Martin Dorsch and the other Frodsham team members designed and produced the missing elements and extensively tested “B” by 2012. During that time, the clock consistently demonstrated remarkable stability and accuracy that was within the parameters of Harrison’s claim.

On April 18th 2012, Clock B was delivered to the Royal Observatory in Greenwich for trial under the supervision of Jonathan Betts, then Senior Specialist in Horology and Rory McEvoy, Curator of Horology for the National Maritime Museum. Initial informal trials repeatedly yielded results within “1 in 100”. After some trial and adjustment the clock’s tamper-proof case was sealed with wax impressions made by representatives of the National Physical Laboratory and the Worshipful Company of Clockmakers. On January 6th 2015, they returned to meet senior Museum staff and witness that the clock was running and showing UTC -1/4 second to begin an official 100-day trial. The trial concluded April 16th, when the aforementioned attested to the security of the clock and the results of the 100-day trial. These signatories confirmed that Clock B, a mechanical pendulum clock working in normal atmosphere, remained within 5/8th of a second from its start for the entirety of the trial. No rate was applied. Harrison’s claim was reasonable and correct.