Observatory regulator, made by Thomas Tompion

In 1675 King Charles II (1660-85) issued a Royal Warrant enabling an observatory to be built at Greenwich. The building was designed by the architect Sir Christopher Wren (1632-1723), and John Flamsteed (1646-1719) was appointed as the first 'Astronomer Royal'.Sir Jonas Moore (1617-79), who supervised the construction of the building, commissioned two specially designed regulators from the leading London clockmaker at the time, Thomas Tompion, with innovative dead-beat escapements designed by Richard Townley, a clockmaker from Burnley in Lancashire.The chapter ring is calibrated in hours, with an outer ring divided into minute divisions, all numbered and calibrated from 1 to 60 twice (that is, for a minute hand completing one rotation in two hours). The subsidiary dial above the centre is for seconds, divided into single seconds and also numbered from 1 to 60 twice (for a second hand completing one rotation in two minutes).Above the Roman numeral 'VI' is a silver plate inscribed, 'Sir Jonas Moore caused this movement with great care to be made Anno 1676 by Thomas Tompion'. At the top of the plate is the inscription 'Motus Annus' indicating that a single wind will keep the clock running for a whole year.The movement is furnished with maintaining power to keep the clock running during winding; evidently they were never meant to stop from one year to the next. When the clock was set up in Greenwich it had a thirteen-foot long pendulum, which took two seconds to complete each swing. After initial problems and adjustments made to the escapement, Flamsteed recorded that the clocks were accurate to within eight seconds per month.The other Tompion clock for the Royal Observatory survives, and is held at the National Maritime Museum, Greenwich.