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The Encyclopedia of Horology

Marine chronometer · Two-day marine chronometer

Thomas Mercer Two-Day Marine Chronometer No. 23531

Partially verified

This two-day marine chronometer, numbered 23531, is signed by Thomas Mercer Ltd. It is constructed with a brass full-plate fusee movement featuring maintaining power, an Earnshaw-type spring detent escapement, a split compensated balance, and a helical hairspring. The chronometer is housed within a brass bowl featuring a sliding winding-hole shutter, suspended by a gimbal mount, and enclosed in a square, glazed mahogany deck box. The silvered 4.25-inch dial displays Roman numerals, an outer minute track, a subsidiary seconds dial, and a 56-hour power reserve indicator. A brass plaque on the box is inscribed with “Nils.V.Dahl, Drottningtorget 10, Malmo. Sweden” and the serial number, which the auction description associates with the instrument's maritime service. The instrument is recorded as being in working order.

The Thomas Mercer two-day marine chronometer in its mahogany deck box, showing the silvered dial and internal identification plaque.
The Thomas Mercer two-day marine chronometer in its mahogany deck box, showing the silvered dial and internal identification plaque. — Vintage Clocks UK. Rights pending — permission not yet requested. Original source

Catalogue identity

Source
vintageclocks.uk
Category
Marine chronometer · Two-day marine chronometer
Maker / attribution
Thomas Mercer Ltd
Reference
Not recorded
Catalogue / lot identifier
Jn57
Source-reported date
Not established
Source-reported place
Not established
Source-reported serial
23531

Source-reported attribution and specifications are not independent authentication. A listing does not establish present ownership, current display, availability or permission to reproduce.

Object description

Dial and Housing

The chronometer features a 4.25-inch silvered dial signed by Thomas Mercer Ltd. The dial layout includes Roman numerals for the primary time display, an outer minute track, and a subsidiary seconds dial. A power reserve indicator, marked with 56 hours, is integrated into the upper portion of the dial, providing a state-of-wind indication. Blued steel hands are used for time and indication display.

The movement is secured within a brass bowl that incorporates a sliding shutter for the winding hole. This bowl is mounted in a gimbal, which allows the chronometer to remain level despite the movement of a vessel. The entire assembly is housed in a square mahogany deck box featuring a glazed lid for viewing the dial.

Evidence for this section
  • “Features a 4.25-inch silvered dial signed by Thomas Mercer Ltd.”
  • “a 56-hour power reserve indicator (state-of-wind)”
  • “Encased in a brass bowl with a sliding winding-hole shutter, suspended on a gimbal mount. This entire assembly is nested inside a square, glazed mahogany deck box.”

Movement and Escapement

The technical operation of the chronometer relies on a brass full-plate fusee movement, which incorporates maintaining power to ensure accuracy during winding. The timekeeping regulation is managed by an Earnshaw-type spring detent escapement. This mechanism is paired with a split compensated balance designed to minimize the effects of temperature variations on the timekeeping rate.

A steel helical hairspring provides the restoring force for the balance assembly.

Evidence for this section
  • “Powered by a brass full-plate fusee movement with maintaining power.”
  • “It utilises a highly precise Earnshaw-type spring detent escapement alongside a split compensated balance and a helical hairspring.”

Provenance and Inscriptions

The mahogany deck box is fitted with a brass plaque identifying “Nils.V.Dahl, Drottningtorget 10, Malmo. Sweden” alongside the serial number 23531.

Additional documentation is present within the box in the form of a sticker from L. J. Harri, a chronometer maker based in Amsterdam, which includes the instrument's serial number and a maintenance date notation.

Evidence for this section
  • “The box is fitted with a brass plaque inscribed “Nils.V”, which likely links the instrument to the specific vessel or shipping company it navigated for during or after the war.”
  • “The “V” is highly likely an abbreviation for a prominent shipping family surname or company.”

Open research questions

  • What is the specific date of manufacture for chronometer number 23531 according to Thomas Mercer production records?
  • Did the entity Nils V. Dahl operate as an importer or a shipping line, and can their specific vessel list be confirmed?

Source evidence

Recorded claims and source quotations for Thomas Mercer Two-Day Marine Chronometer No. 23531
FieldSource-reported valueSource quotation
MakerThomas Mercer Ltd“manufactured by Thomas Mercer Ltd”
Serial number23531“No. 23531”
Movement typeBrass full-plate fusee“brass full-plate fusee movement”
EscapementEarnshaw-type spring detent“Earnshaw-type spring detent escapement”
Dial size4.25 inches“4.25-inch silvered dial”
Power reserve56 hours“56-hour power reserve indicator”
Dimensions17cm x 18cm x 18cm“Measures 17cm high by 18cm wide & 18cm deep”
SKUJn57“SKU: Jn57”

Visible details

  • The dial features a 56-hour power reserve indicator positioned at the 12 o'clock location.
  • The mahogany deck box lid displays a brass identification plaque inscribed with the retailer's details and the serial number.
  • The brass bowl contains a sliding shutter to protect the winding hole.
  • Internal stickers indicate the piece was serviced by L. J. Harri of Amsterdam.

Research qualifications

  • The exact historical vessel or shipping line associated with the “Nils.V” marking remains unverified.
  • The manufacturing date of the chronometer is not explicitly stated in the source text.

Photograph identity and source facts were screened before import; rights clearance remains pending.

Consulted source

The Thomas Mercer Chronometer No. 23531 is a historic two-day marine chronometer manufactured by Thomas Mercer Ltd

Reviewed 2026-11-02 · Record 8d9f8786f5

Terms in this record

Glossary explanations for terms named in this object’s record.

Other two-day marine chronometer records