Studying the numbering sequence prepared by Anthony Randall and published in his book, The Time Museum Catalogue of Chronometers,
the present watch can be dated more or less exactly to 1803. Thomas Earnshaw claimed to have invented the spring detent escapement in 1781, after he discovered inherent issues with the oiled pivots of the pivoted detent escapement. Previously collaborating with Brockbanks for the construction of chronometers with the pivoted detent escapement, Earnshaw and Brockbanks had a disagreement and Earnshaw approached Thomas Wright with the designs of his new escapement. At the time, Thomas Wright was watchmaker to King George III and, as Earnshaw lacked funds to apply for the one hundred guinea patent for his invention, the pair entered an agreement whereby Wright would apply and pay for the patent in his name. Earnshaw would then make movements for any other watchmakers who ordered them, adding a one guinea fee payable to Wright to cover the patent cost. The patent, no. 1354, was filed in 1783. Earnshaw listed names of makers for whom watches were made under this agreement and these included: Barraud, Frodsham, Margetts and Vulliamy. For a discussion of Earnshaw’s patent see: Rupert T. Gould, The Marine Chronometer
, Chapter VIII, pp. 189-193.
From around the mid-1790s, Earnshaw fitted his chronometers with plain steel balances, spiral springs and 'sugar tongs' bi-metallic compensation (although he also continued to use the combination of compensation balance and helical spring). The arms of the ‘sugar tongs’ embrace the outer coil of the spring, altering their shape and length, the curved ends moving closer together or further apart with changes in temperature, thus compensating for the effect caused by these changes on the balance and spring. The timekeeping may not have been so constant, but the balance was lighter and the pivots therefore less susceptible to damage. This set-up would also have made the watch easier to regulate as compared to chronometer balances with timing screws. Shortly before 1800, Earnshaw ceased gilding the plates and blueing the steel parts of many, although not all, of his movements.