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The Encyclopedia of Horology

Component · Compensation balance

Compensation balance with Kullberg's auxiliary

Partially verified

This chronometer compensation balance with Kullberg's auxiliary compensation is preserved in the Science Museum Group collection under object number 1929-71, credited to maker Thomas Mercer. The museum records the component's materials as bi-metallic arms intended for use with a steel balance-spring, measuring 5 mm by 40 mm by 37 mm and weighing 0.0091 kg. The assembly displays a central crossbar with a perforated center boss, curved bimetallic rim sections, large cylindrical brass weights, and slotted cylindrical timing nuts positioned on threaded terminal extensions.

Oblique view of the compensation balance with Kullberg's auxiliary showing the bi-metallic rim and weights
Oblique view of the compensation balance with Kullberg's auxiliary showing the bi-metallic rim and weights — Science Museum Group. Rights pending — permission not yet requested. Original source

Catalogue identity

Source
collection.sciencemuseumgroup.org.uk
Category
Component · Compensation balance
Maker / attribution
Thomas Mercer
Reference
Not recorded
Catalogue / lot identifier
1929-71
Source-reported date
Not established
Country
Not established

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

Identity and Institutional Classification

In the Science Museum Group collection, this component is recorded under object number 1929-71 with the title 'Compensation balance with Kullberg's auxiliary'. The record classifies the item under 'Category: Time Measurement' and lists its functional type as 'type: compensation balance for chronometer'.

The catalog entry names 'maker: Thomas Mercer' and lists the credit line as 'credit: Thomas Mercer Ltd.'.

Evidence for this section
  • “Compensation balance with Kullberg's auxiliary maker: Thomas Mercer”
  • “Category: Time Measurement”
  • “Object Number: 1929-71”
  • “type: compensation balance for chronometer”
  • “credit: Thomas Mercer Ltd.”

Physical Specifications and Construction

Recorded measurements for the balance laid flat are '5 mm x 40 mm x 37 mm, 0.0091 kg'. The materials entry indicates 'arms: bi-metallic' and records 'balance-spring (for use with): steel'.

Visual examination of the assembly shows a central crossbar with a circular central boss pierced by three drilled perforations, along with slotted cylindrical brass nuts mounted at the ends of the crossbar on threaded studs. Two large cylindrical brass weights are attached to the bimetallic rim segments, and auxiliary compensation segments with slotted mounting arms and set screws are positioned along the inner perimeter of the rim.

Evidence for this section
  • “overall (laid flat): 5 mm x 40 mm x 37 mm, 0.0091 kg”
  • “arms: bi-metallic”
  • “balance-spring (for use with): steel”
  • “Central crossbar features a circular central boss with three drilled perforations.”
  • “Slotted cylindrical brass nuts are mounted at the ends of the crossbar on threaded studs.”
  • “Two large cylindrical brass weights are affixed to the bimetallic rim segments.”
  • “Auxiliary compensation segments with slotted mounting arms and set screws are visible along the inner perimeter of the rim.”

Source Documentation and Assembly Context

The museum record does not record a date of manufacture, place of origin, or serial number for the object. While the accession identifier is designated as '1929-71', detailed provenance or acquisition history is not detailed in the source text.

The physical balance staff and balance spring mentioned in the compatibility specification ('for use with: steel') are absent from the pictured assembly.

Evidence for this section
  • “Object Number: 1929-71”
  • “balance-spring (for use with): steel”

Open research questions

  • Does the museum acquisition file for 1929-71 record whether the balance was gifted or purchased directly from Thomas Mercer Ltd. as a demonstration model or spare chronometer part?
  • Do physical inspection and dismantling reveal maker marks, batch numbers, or assembly punch marks beneath the auxiliary segments or weights?

Source evidence

Recorded claims and source quotations for Compensation balance with Kullberg's auxiliary
FieldSource-reported valueSource quotation
MakerThomas Mercer“maker: Thomas Mercer”
Object Number1929-71“Object Number: 1929-71”
TypeCompensation balance for chronometer“type: compensation balance for chronometer”
Arm MaterialBi-metallic“arms: bi-metallic”
Spring Material CompatibilitySteel“balance-spring (for use with): steel”
Measurements5 mm x 40 mm x 37 mm, 0.0091 kg“overall (laid flat): 5 mm x 40 mm x 37 mm, 0.0091 kg”
Museum CreditThomas Mercer Ltd.“credit: Thomas Mercer Ltd.”
Collection CategoryTime Measurement“Category: Time Measurement”

Visible details

  • Central crossbar features a circular central boss with three drilled perforations.
  • Two large cylindrical brass weights are affixed to the bimetallic rim segments.
  • Slotted cylindrical brass nuts are mounted at the ends of the crossbar on threaded studs.
  • Auxiliary compensation segments with slotted mounting arms and set screws are visible along the inner perimeter of the rim.

Research qualifications

  • No manufacturing date or place of origin is provided in the source text.
  • Balance staff and balance spring are absent from the pictured assembly.

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

Consulted source

Compensation balance with Kullberg's auxiliary | Science Museum Group Collection

Reviewed 2026-10-21 · Record 54263c356e

Terms in this record

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