According to Anthony Randall, in The Time Museum Catalogue of Chronometers, 1991, p. 28, Edward John Dent was the first to publish an account of the secondary error of compensation, or middle temperature error, in the Nautical Magazine of 1833. He was also one of the pioneers in looking for a practical solution to the problem.On March 21, 1842, Dent applied for a Patent to be entitled Certain Improvements in Chronometers and other Timekeepers. This Patent, No. 9302, covered various designs of compensation balances and the invention of a Remontoire for use in Marine chronometers. One of the compensation balances became known as Dent's "staple" or "hurdy-gurdy" on account of the arrangement of "U" shaped bimetallic pieces carried on the ends of the cross-bar. Dent used this type of balance both for marine chronometersnd carriage clocks. Some of the earliest chronometers fitted with it, were used with great success for the longitude determination between Altona and Pulkowa in1843-1844. Dent was awarded the Royal Warrant, as supplier of clocks and chronometers to Queen Victoria, in 1841.Charles Frodsham, (1810-1871). He was the most celebrated of the numerous Frodsham family of watchmakers and was a prominent maker of very high grade chronometers and watches. He devised in 1868, a form of electrical contact for taking signals for chronometers. The company he founded continued after his death. At some time before the middle of the last century, the company began making lever escapement and chronometer escapement watches of the very highest quality and continued to do so until thoutbreak of war in 1939. For the 1851 exhibition, they introduced a three-quarter plate calibre which they marked "AD.Fmsz", which continued subsequently to be put on all their highest grade work. The significance of "AD.Fmsz", is said to be found by putting the name of Frodsham against numbers thusHence FMSZ gives the date 1850.During the first part of this century the firm was closely connected with Nicole Nielsen who made most of the movements, including some of the most perfect tourbillons ever made, and which still perform with almost unrivalled accuracy. While other watches became increasingly ugly during the 19th and 20th century, Frodsham watches are almost always elegant and well proportioned and, even as late as 1914, some of them, with engine-turned silver dials, were worthy of Breguet.