English temperature compensation pocket watch Circa 1790

Gold pocket chronometer by Thomas Earnshaw
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An English pocket chronometer by Thomas Earnshaw with sugar tongs– temperature compensation for balance spring, circa 1790.
18 Carat rose gold polished case with case maker punch mark IM and jumping lids on the front and backside. Signed enamel dial with radial Arabic numerals, auxiliary seconds, and gold Breguet hands. Full plate movement, frosted, gilt, signed, and keywind; with chain/fusee, moulded pillars, spring detent escapement according to Thomas Earnshaw, three-arm steel balance, bimetallic sugar tongs– temperature compensation for blued balance spring, and florally engraved balance cock.
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Diameter: 61 mm
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Weight: 175 g
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Signed: Robert Best, London
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Robert Best,
Robert Best trained from 1778 to 1782 with Thomas Earnshaw Snr and then worked as a foreman in the workshop of renowned chronometer maker John Brockbank at 5 Cowpers Court; around 1790 Best had his own business at 4 WhiteLion Court, Birchin Lane.
After 1798 he was located at 4 Sweetings Alley and after 1810 at 1 Windsor Place, St. Paul’s; Best was a member of the Clockmakers company from 1783 until 1820.
Around 1796 Best was bankrupt and emigrated to Constantinople for some time; he returned to support his master Earnshaw’s claim regarding his chronometer escapement, which was heavily contested by John Arnold’s son John Roger Arnold and Dr Maskelyne, the resident Astronomer Royal during the Board of Longitude’s enquiries in 1804. Best was, together with Joseph Watkins, Charles John Cope und William Frodsham, also in a partnership with P.P. Barraud and George Jamison for the production of Mudge chronometers.
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The case of the watch was probably made by James Macklin at 7 Plumtree Street, Bloomsbury; its movement closely resembles Barraud’s watch E3 /1803/218 (delivered by Earnshaw); this is the same with the movements of Earnshaw’s watch no. 30175 and other Earnshaw watches. The author’s assumption that this is clearly a watch produced by Thomas Earnshaw Snr is confirmed by Earnshaw himself – in his famous pamphlet, he states that many of his pocket chronometers with spring detent escapement bore the signatures of distributors and mentions, among others, Robert Best in this context.