John Arnold

John Arnold (born 1736 probably in Bodmin, Cornwall – died 1799 in London) was an English watchmaker and inventor.

John Arnold was the first to design a watch that was both practical and accurate, and also brought the term "Chronometer" in to use in its modern sense, meaning a precision timekeeper. His technical advances enabled the quantity production of Marine Chronometers for use on board ships from around 1782. The basic design of these, with a few modifications unchanged until the late twentieth century. With regard to his legacy one can say that both he and Abraham-Louis Breguet largely invented the modern mechanical watch. Certainly one of his most important inventions, the Overcoil balance spring is still to be found in most mechanical wrist watches to this day.

From around 1770, Arnold continued to develop portable precision timekeepers, almost from the point where John Harrison ended his work on precision timekeeping. Compared to Harrison's watch, Arnold's basic design was simple whilst consistently accurate and mechanically reliable. Importantly, the relatively conventional movement design facilitated its production in quantity at a reasonable price while facilitating easier maintenance.

Three elements were essential to this achievement:

• A detached escapement, which gave minimal interference with the vibrating balance and balance spring
• A balance design that enabled compensation for the effect of temperature on the balance spring
• A method for adjusting the balance spring, so that the balance oscillates in equal time periods, even through different degrees of balance arc