Marine chronometer · Two-day boxed marine chronometer

Thomas Mercer Two-Day Marine Chronometer, No. 17989

Partially verified

This two-day marine chronometer by Thomas Mercer Ltd of St Albans is housed in a fitted wooden transport box with brass gimbals. The silvered dial features black Roman hour numerals, blued steel hands, an up-and-down state-of-wind indicator dial, and a continuous subsidiary seconds register. The seconds dial incorporates an unusual open cut-out displaying the seconds wheel mechanism. According to the seller, the brass movement features a chain fusee and spring detent escapement, bearing serial number 17989, which is associated with production around the 1940s.

Oblique view of the silvered dial, gimbals, and wooden box of the Thomas Mercer chronometer — Sellingantiques / Finchingfield Antiques. Rights pending — permission not yet requested. Original source

Catalogue identity

Source: www.sellingantiques.co.uk
Category: Marine chronometer · Two-day boxed marine chronometer
Maker / attribution: Thomas Mercer Ltd
Reference: SA683094
Catalogue / lot identifier: Source URL identifies the listing
Source-reported date: circa 1940s
Country: United Kingdom
Source-reported serial: 17989

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 Visual Architecture

The instrument features a circular silvered dial fitted with blued steel spade hands set against black Roman numeral hour markers. Positioned below the 12 o'clock marker is an up-and-down state-of-wind indicator dial, paired with a subsidiary seconds register positioned at 6 o'clock.

The dial incorporates an open cut-out aperture at the seconds register through which the brass gearing of the seconds wheel is visible. Dial inscriptions include 'THOMAS MERCER LTD / ST. ALBANS, ENGLAND' and movement number '17989' located within the state-of-wind indicator register.

Evidence for this section

“Silvered dial with state-of-wind subdial below 12 o'clock and an open aperture at the 6 o'clock seconds register revealing brass gearing”
“Dial signed 'THOMAS MERCER LTD / ST. ALBANS, ENGLAND' and numbered '17989' within the state-of-wind indicator”
“Spade-style blued steel hands against black Roman numeral hour indices”
“The silvered dial has a very unusual cut out where the seconds wheel can be seen as it steps out the seconds.”

Reported Movement and Technical Specification

According to the seller's description, the movement is of two-day duration and incorporates a chain fusee along with a spring detent escapement. As the movement plates and interior mechanism are enclosed within the brass bowl, these specific technical details derive from the listing text rather than direct examination.

The brass bowl is mounted in brass gimbals inside an open wooden box, complete with visible brass mounting hardware and a winding key post.

Evidence for this section

“The movement is of 2 day duration with a chain fusee and spring detent escapement”
“Gimballed brass bowl mounted inside an open wooden box with brass hardware and winding key post visible”

Casework and Chronological Context

The chronometer is housed within an inner wooden box and is reported by the seller to include its original outer 'cutter travel box' equipped with a leather strap and buckle. The outer travel container is not shown in the primary photograph.

Dating for the instrument varies across the listing source: the seller states serial number 17989 suggests a 1947 production date, the declaration dates the piece to the 1940s, and the listing header cites 1920–1940.

Evidence for this section

“It comes complete with its original cutter travel box.”
“The travel case has a leather strap with buckle.”
“I has the number 17989 which we believe dates the clock to 1947.”
“Finchingfield Antiques has dated this Thomas Mercer Marine Chronometer to the 1940s.”
“Thomas Mercer 2 Day Chronometer 1920 - 1940”

Open research questions

Do Thomas Mercer manufacturing records confirm whether serial number 17989 was completed in 1947 or earlier between 1920 and 1940?
Was the cut-out dial aperture exposing the seconds wheel a standard Thomas Mercer factory demonstration feature or an aftermarket modification?
Are any military Broad Arrow marks or hydrographic survey numbers stamped on the gimbal ring, brass bowl, or outer travel box?

Source evidence

Recorded claims and source quotations for Thomas Mercer Two-Day Marine Chronometer, No. 17989
Field	Source-reported value	Source quotation
Serial number	17989	“I has the number 17989”
Escapement	Spring detent	“chain fusee and spring detent escapement”
Duration	2 day	“The movement is of 2 day duration”
Dial cut-out	Aperture showing seconds wheel	“The silvered dial has a very unusual cut out where the seconds wheel can be seen”
Travel case accessory	Leather strap with buckle	“The travel case has a leather strap with buckle.”

Visible details

Silvered dial with state-of-wind subdial below 12 o'clock and an open aperture at the 6 o'clock seconds register revealing brass gearing
Dial signed 'THOMAS MERCER LTD / ST. ALBANS, ENGLAND' and numbered '17989' within the state-of-wind indicator
Gimballed brass bowl mounted inside an open wooden box with brass hardware and winding key post visible
Spade-style blued steel hands against black Roman numeral hour indices

Research qualifications

Date is estimated by the seller (stated variously as 1920-1940, 1940s, or 1947)
Outer cutter travel box mentioned in the listing description is not visible in this photograph

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

Consulted source

Thomas Mercer Marine Chronometer 1920 - 1940 | Sellingantiques.co.uk

Reviewed 2026-10-21 · Record 689ebe4fc8

Terms in this record

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

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