Pocket chronometer no. 309 by Thomas Earnshaw

Record summary

Held and catalogued by Royal Museums Greenwich (object number ZBA4669), this is a pocket chronometer by Thomas Earnshaw, made in England, dated 1790s. The Atlas places it in the Precision & Scientific Horology period (1750 – 1850) of its Pocket Watches collection. Materials and techniques recorded by the source: metal; enamel. Recorded dimensions: Overall: 81 mm x 59 mm x 26 mm. The record is illustrated with 4 photographs.

Assembled from the source record's structured fields. Dates and attributions are given as the source states them; where a field is missing the Atlas leaves it blank rather than estimating.

Catalogue description

Atlas type guide

Pocket chronometers and precision watches

A pocket chronometer is a watch built to observatory standards, traditionally with a detent escapement like a marine chronometer. English makers such as John Arnold and Thomas Earnshaw made the first pocket chronometers in the 1780s. In the nineteenth century the term increasingly referred to any watch that had passed official rating trials at observatories in Kew, Neuchâtel, Geneva or Besançon, and the Swiss lever chronometer became dominant.

Tourbillon and karrusel watches belong to the same world of precision. Breguet patented the tourbillon in 1801 to average out positional errors; Bahne Bonniksen's karrusel (1892) was a cheaper English alternative. Rating certificates (bulletins de marche) that accompany such watches are historical documents in their own right.

General guidance written by the Atlas editors about this kind of object. It is not a statement about this particular piece; for that, rely on the source record above and on physical examination.

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