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The Encyclopedia of Horology

Pocket watches · Escapement

Pocket Chronometers

Verified

High-precision pocket watches fitted with a detent (chronometer) escapement, built to marine or observatory rating standards.

Mechanism

The balance unlocks the escape wheel once per revolution via a spring detent, receiving a single clean impulse and remaining otherwise entirely free of the train, maximising isochronism at the cost of shock resistance.

Typical characteristics

  • Spring or pivoted detent escapement
  • Helical or spiral hairspring with compensation balance
  • Often boxed with a gimbal mount for marine use

Identification characteristics

  • Detent and impulse roller visible on the balance side of the movement
  • Certificates or engraved observatory trial results on high-grade examples

Collector significance

The precision benchmark against which lever watches were long measured, and essential to the history of marine navigation.

Known variations

  • Spring detent (pocket) chronometer
  • Pivoted detent chronometer
  • Deck watch

Related photographs

Description of the Le Roy detent escapement mechanism 14 August 1748
Description of the Le Roy detent escapement mechanism 14 August 1748 — Academie des Sciences, France 14 August 1748, Public domain. Wikimedia Commons file page
British Museum Marine Chronometer 1
British Museum Marine Chronometer 1 — Photograph by Mike Peel (www.mikepeel.net)., CC BY-SA 4.0. Wikimedia Commons file page
Diagram of the chronometer detent escapement Britten's Clock and Watchmaker's Handbook 9th Edition 1896
Diagram of the chronometer detent escapement Britten's Clock and Watchmaker's Handbook 9th Edition 1896 — F.J. Britten, Public domain. Wikimedia Commons file page

No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.

Sources & references

  1. Gould, R. T., The Marine Chronometer: Its History and Development

Where sources disagree, the disagreement is stated rather than resolved silently.