Institutions – Certification bodies & labs

CERTIFICATION OF CHRONOMETERS ACCORDING TO ISO 3159

Established in 1976 by the International Organization for Standardization (ISO), ISO 3159 is the international benchmark for measuring the accuracy of mechanical watches.

It ensures that the title of chronometer is based on objective criteria, evaluated according to a rigorous and reproducible protocol. By imposing a uniform framework on a global scale, this standard strengthens the credibility of certifications and highlights the watchmaking expertise rooted in mastery of time.

Purpose of the Standard

The primary goal of ISO 3159 is to define the control requirements used to evaluate the precision of chronometers under standardized testing conditions.
More specifically, it aims to:

  • Ensure chronometer accuracy under varied conditions of use.
  • Standardize testing methods to guarantee the comparability of results across different models and manufacturers.
  • Promote transparency in manufacturing and certification processes, enabling users to choose instruments that meet measurable criteria of reliability.

Testing Protocol

The tests defined by ISO 3159 apply to mechanical wristwatch movements with balance and hairspring regulation. The protocol spans fifteen days, during which each movement is tested in five different positions and at three reference temperatures: 8 °C, 23 °C, and 38 °C.
At the end of these tests, the performance of each movement is evaluated according to several criteria (mean daily rate, variation, recovery, influence of temperature, etc.). The most well-known of these establishes that the average daily rate must fall between –4 and +6 seconds per day.

Advantages of ISO 3159

  • Guaranteed accuracy: Watches tested according to the standard meet strict criteria, ensuring reliable timekeeping performance.
  • International harmonization: By applying an identical protocol worldwide, the standard facilitates comparison and recognition of chronometric performance.
  • Continuous improvement: The definition of measurable thresholds encourages manufacturers to constantly optimize the quality and consistency of their movements.
  • Official recognition: Watches compliant with ISO 3159 may receive an independent certification recognized internationally.

Certification Bodies

In Switzerland, two institutions are authorized to issue chronometer certificates in accordance with ISO 3159: