John Arnold, an English watchmaker and inventor was born in Bodwin, Cornwall, England in 1736 and was the first to design a watch that was both practical and precise. He also coined the term "chronometer" to refer to a precision timekeeper in its contemporary definition. From around 1782, his technological improvements enabled the mass manufacture of marine chronometers for use on-board ships.
At an early age, John Arnold learnt under his father, who was also a clockmaker. He left England when he was 19 years old to work as a watchmaker in The Hague, Holland, before returning to England in 1757.
In 1762, he met William McGuire in St Albans, Hertfordshire, and repaired a repeating watch for him. Arnold made enough of an impression on McGuire that he was granted a loan, allowing him to open a watchmaking shop in Devereux Court, Strand, London.
Arnold was granted permission to present King George III with a half-quarter repeating cylinder escapement watch placed in a ring in 1764.
Around 1768, Arnold constructed another watch for the King which was given the designation "Number 1" by Arnold —something he did when the watches he built was regarded as significant.
Arnold altered John Ellicott's centre seconds watch for Astronomer Royal Nevil Maskelyne, which he lent to Astronomer William Wales in 1769 to test the feasibility of Maskelyne's Lunar distance method for determining the ship's longitude during the Transit of Venus expedition to the West Indies.
From 1772 – 1775 Arnold created a new type of pocket watch. He made 35 of them.
During the same year he obtained a patent for a new type of compensatory balance with a bimetallic spiral at the centre.
Arnold modified his chronometer in 1777 making it larger to accommodate the new “T” Balance that worked with his pivoted detent escapement and patented helical spring. Since it was a one-of-a-kind innovative design, the first chronometer was signed "Invenit et Fecit".
From February 1, 1779, through July 6, 1780, the Royal Observatory in Greenwich put Arnold 36 to the test in a variety of ways, including wearing it and carrying it around. The watch outperformed all expectations in terms of accuracy.
Between 1779 and 1782, Arnold perfected the shape of his chronometer watches which he patented in 1782.