This regulator is known as the ‘RAS’ (Royal Astronomical Society) or ‘Late’ regulator, to distinguish it from the earlier wooden precision pendulum clocks made by Harrison in the 1720s. It was his last word in fixed, land-based, timekeeping design and Harrison himself suggested it might, if properly adjusted, be capable of keeping time to within one second in 100 days. Made at about the same time as H3 (1740-1759), it is the fixed, pendulum controlled ‘sister’ to that timekeeper and has much in common with it. The clock has a grasshopper escapement, a 30 second remontoir, and runs without any lubrication. As far as is known the RAS regulator was never finally adjusted by Harrison, though it may be the clock shown behind him in his portrait, in a wooden case with a gridiron pendulum. The pendulum was a restoration of Gould’s (made by James Agar-Baugh) in 1928.