Technology in the film

Poor clock oils were a common problem in the 18th century, which was one of the main reasons why timepieces would break down. Harrison created a clock that didn't require oil, rather than focusing on ways to make the oil better. Later, when he took on the challenge of creating a maritime timekeeper, creative thinking of this kind would be crucial.

Because of the clock's two interconnected swinging balances, it is unaffected by the motion of a ship; it is essentially a portable version of Harrison's precision wooden clocks. 

Harrison and H1 were brought on board the HM ship Centurion in May 1736 as it prepared to depart for Lisbon. The purpose was to test H1 in a real-world situation.

Harrison's clock had a rough start to the trip to Lisbon. Yet by the time they got to Lisbon, the machine was operating considerably more dependably. The outcome of this voyage was considerably better.

Back in London, the result of the Lisbon case gave some hints that Harrison might be qualified for a reward under the Longitude Act. A formal meeting of the Commissioners of Longitude was requested by the Navy.

Hence, on June 30, 1737, eight of them gathered to talk about Harrison's "strange device." The commissioners approved a £500 payout. For Harrison to be able to construct a better clock, £250 had to be paid upfront. He pledged to complete this task in two years.

Soon after the Lisbon trial, Harrison migrated to London and constructed his second sea-clock in the two years promised. H2 was never utilized, however, because Harrison had discovered a fundamental flaw: the bar balances periodically failed to counteract ship motion, a flaw that could have been fixed if the balances were circular.

In 1740, Harrison started working on his third try, H3, and he wouldn't finish it for another 19 years. After five years of use and testing, it became clear that the clock would struggle to maintain the necessary degree of accuracy. Harrison was compelled to alter and adapt significantly.

Harrison recruited John Jefferys to design a watch with a radically different form of balance sometime between 1751 and 1752. Harrison incorporated it into his fourth longitude timekeeper, H4, because it performed well.

The pocket watch was not considered to be a serious, accurate timekeeper in the 1750s. H4 was initially misunderstood as a huge pocket watch, although it was actually quite different.

The quick ticking of its timepiece reveals the secret. Since H4's huge balance beats faster and with greater oscillations than a regular watch, it ticks five times each second.

The Commissioners provided William Harrison's authority to plan for a voyage to Jamaica in 1761 so that he could test the H4 timekeeper there. The trial looked to proceed smoothly. William utilized it to anticipate an earlier landfall at Madeira than what the crew had anticipated on the way out. The captain was so impressed by this that he requested to purchase an additional timekeeper.

This website does a great job detailing every H1-H5 as well as the details of John Harrison's life! Other websites detailing the history can be found in the sources tab of the website.