The Chronometer Department at the Royal Observatory, Greenwich had its origins back in 1766 when the Board of Longitude ordered the first chronometer trials to test John Harrison’s chronometers at sea. Over the next 50 years, chronometers continued to be tested for the Board and in 1818 a new Longitude Act created a post of Superintendent of Chronometers, initially held by Thomas Hurd (Hydrographer of the Navy). In 1821, the post was transferred to the Astronomer Royal, John Pond, and the Royal Greenwich Observatory became responsible for testing, rating and issuing the Admiralty’s chronometers.

In June 1821 the Admiralty ordered the first of a series of annual trials of chronometers at the Observatory to improve the standard of chronometers purchased by the Navy. Trials ran until 1836 and Pond and the Royal Observatory were responsible for overseeing the trials as well as administering the issuing and receiving of chronometers to ships. Pod’s successor, George Airy, managed to drop some of the administrative work but commenced a new series of chronometer trials in 1840, with separate trials for watches from 1888-1889. These formal trials continued until the outbreak of war in 1914, when they were permanently suspended, after which time work was confined to rating and testing chronometers and watched that the Admiralty already owned.

In 1936 Humphry Smith was appointed the new Head of the Time Department and the following year he established the first workshop for the repair and adjustment of watches and chronometers. With the outbreak of World War 2, the Time Department was effectively split in two, as it was decided to remove the entire chronometer and watch testing and repair to a safer area. In September 1939, George Rickett (as Officer-in-Charge of the new Chronometer Depot) was evacuated with the chronometers, a small team, and the workshop staff, first to Bristol, then to Lynchetts, a requisitioned house in Bradford on Avon. Meanwhile, a duplicate Time Service was set up at the Magnetic Observatory, Abinger. At Lynchetts, chronometer workshop staff gradually increased from five in 1941 to ten in 1944, and in December 1944 a new watch repair shop was completed.

Chronometer operations continued at Bradford on Avon until 1948 when the Chronometer Department, as it was now known, became one of the first departments to move to RGO’s new premises at Herstmonceux Castle. Initially, paperwork for the department was done in an office on the north side of the Library landing in the castle, rating of the chronometers in varying conditions of temperature took place in rooms on the lower floor of the west-wing of the castle, while the workshop occupied a wartime hutment. In 1957, the workshop moved into a purpose-built Laboratory on the first floor of the West Building, while the office and rating section remained in the castle until 1962.