English gold chronometer with spring detent escapement Circa 1800

Gold pair cased pocket watch 
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A very fine and rare English, gold pair cased pocket chronometer, circa 1800.
With Earnshaw’s spring detent escapement and Earnshaw’s Z compensation balance.
Made by Thomas Earnshaw, Invenit et Fecit, No. 429 of the sort/2660. The case is made by Thomas Carpenter with London hallmarks for 1800. The outer and inner cases are both polished. White enamel dial, radial Roman numerals, outer minute track, subsidiary seconds. With gold heart and poker hands.
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A gilt full plate movement with cylindrical pillars, fusee and chain with Harrison’s maintaining power, Earnshaw spring detent escapement, escape wheel jewelled with end stones in screwed chatons, Earnshaw’s Z bimetallic compensation balance with sliding timing weights and two steel mean time screws, single-footed cock with endstone in screwed Chaton, free-sprung blued steel helical balance spring. Dial and movement signed and numbered.
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Diameter: 65 mm
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Signed: Thomas Earnshaw  London
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Using Earnshaw’s numbering system, the first number is the number of watches made at that point using Earnshaw’s spring detent escapement. The second number, in this case, 2660, is the total number of watches produced at that point. Thomas Earnshaw (1749-1829) Born in Ashton-Under-Lyne in Lancashire, by 1780 he had the reputation of being a very fine watch finisher. He invented the modern chronometer spring detent escapement towards the end of 1780, a design that he insisted was stolen by Arnold. However, it is likely that Earnshaw and Arnold arrived at their conclusions separately. Earnshaw perfected the fusing together of brass and steel to make laminae for compensation balances which previously had had to be riveted.