Glossary · Regulation

Chronometer error

The difference between an indicated time and the chosen reference time at a stated instant.

Explanation

An error is an offset, whereas a rate describes change in that offset over an interval. Always state the sign convention: for example, error equals indicated time minus reference time, with positive values meaning fast. “Correction to apply” may use the opposite sign. A record without a reference time, date and convention cannot safely support a longitude calculation. This definition uses an explicit analytical convention rather than claiming that every historical rating book used identical terminology.

Diagram

Schematic: chronometer rate record. Rate schematic: error accumulates from daily rate and correction, so a log entry must keep observation time, rate and correction separate.

Photographic reference

E. Barthet No. 10 — gimballed box, L2015-3496 — © The Board of Trustees of the Science Museum / Science Museum Group / The Clockmakers’ Museum, CC BY-NC-SA 4.0 as stated by source; commercial-use permission review pending. Official museum or publication source

E. Barthet No. 10 — dial and canister — © The Board of Trustees of the Science Museum / Science Museum Group / The Clockmakers’ Museum, CC BY-NC-SA 4.0 as stated by source; commercial-use permission review pending. Official museum or publication source

E. Barthet No. 10 — exposed movement — © The Board of Trustees of the Science Museum / Science Museum Group / The Clockmakers’ Museum, CC BY-NC-SA 4.0 as stated by source; commercial-use permission review pending. Official museum or publication source

E. Barthet No. 10, L2015-3496: exact chronometer context, not evidence of a recorded rate or a lunar-distance observation.

Cross-references

Nearby regulation terms

Breguet overcoil: A hairspring whose outer turn is raised and curved over the body of the spring.
Breguet spring: A hairspring with a raised outer coil to improve isochronism.
Chronometer rate: The known daily rate of a marine chronometer.
Chronometer rate book: A record of comparisons used to follow a chronometer’s error over time.
Compensation balance: A balance wheel designed to counteract the effects of temperature changes.