 Upon completion of the run, the clock was measured to have lost only 5/8 of a second, meaning Harrison's design was fundamentally sound.If we ignore the fact that this clock uses materials such as duraluminium and invar unavailable to Harrison, had it been built in 1762, the date of Harrison's testing of his H4, and run continuously since then without correction, it would now ( 2020) be slow by just trunc (((+6556507200)*72.338e-9 round 0)/60) minutes and ((+6556507200)*72.338e-9 round 0) % 60 seconds.Guinness World Records has declared the Martin Burgess' Clock B the "most accurate mechanical clock with a pendulum swinging in free air."