ISO 6426-1:1982

Overview

ISO 6426-1:1982 - Horological vocabulary, Part 1: Technical and scientific definitions - is an international standard that defines the principal technical and scientific terms used in horology. The standard provides about 20 core definitions that apply to time‑measuring instruments (clocks, watches, oscillators) and related devices, and it includes a table summarizing the associated values and units of measurement (SI and practical horological units). Part 2 of ISO 6426 covers technico‑commercial vocabulary.

Key topics

The standard organizes definitions in a logical order and covers fundamental horological concepts such as:

• Time, date, duration - formal description of the time medium and how instants are marked on a time scale.
• State and instrumental correction - the difference between an instrument’s indicated date and a reference date, and the algebraic correction to obtain the reference.
• Rate and instantaneous rate - speed (rate) of a timepiece expressed conventionally in seconds per day (s/d) and the notion of instantaneous vs. average rates.
• Probable rate and probable daily rate - statistically based expected rate under conditions of normal use.
• Drift and deviation - rate change over an interval (drift) and limit values as duration tends to zero (deviation); units may include s‑1, s/d2, or s/(d·a).
• Variations and differences on frequency/period - definitions for Δf, ΔT, and relative differences used to characterize oscillators.
• Chronometric stability - expressed via drift and deviation measures to evaluate short‑, medium‑ and long‑term stability.
• Table of values and units - mapping of defined quantities to SI units and practical horological units (e.g., s, s/s, s/d, Hz).

Applications

ISO 6426-1 is practical for:

• Watchmakers, horologists and bench technicians for clear, standardized terminology when testing, calibrating and documenting timekeeping performance.
• Metrology and testing laboratories reporting rates, drifts and deviations using consistent units (SI and conventional horological units).
• Manufacturers and designers for specifications, quality control and product documentation.
• Standards writers, translators and educators who need authoritative definitions for horological vocabulary.
• Museums and conservators documenting historic timepieces with precise technical terms.

Related standards

• ISO 31/1 (Values and units of space and time) - referenced for SI unit consistency.
• ISO 6426 Part 2 - planned companion standard covering technico‑commercial terms.

Keywords: ISO 6426-1, horological vocabulary, horology, time‑measuring instruments, rate, drift, deviation, seconds per day, SI units, chronometric stability.