CHRONOMETER CERTIFICATION ACCORDING TO THE ISO 3159 STANDARD

Developed in 1976 by the International Organization for Standardization (ISO), the ISO 3159 standard is the international reference for measuring the precision of mechanical watches.

It ensures that the title of Chronometer is based on objective criteria, assessed 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 horological expertise founded on the mastery of Time.

WHAT IS THE PURPOSE OF THE STANDARD?

The main purpose of ISO 3159 is to define the Testing requirements used to assess the precision of Chronometers under standardized test conditions.
More specifically, it aims to:

1. Ensuring accuracy of Chronometers under varied conditions of use.
2. Standardizing test methods, to ensure the comparability of results across different models and manufacturers.
3. Encouraging transparency in manufacturing and certification processes, allowing users to choose instruments that meet measurable reliability criteria.

WHAT IS THE TESTING PROTOCOL?

The tests defined by the ISO 3159 standard concern the Movement of mechanical wristwatches with Balance-Hairspring (balance spring). The protocol extends over fifteen days, during which each Movement is tested in five different positions and at three nominal Temperatures: 8°C, 23°C and 38°C.

At the end of these tests, the Movement’s performance is calculated according to several criteria (average rate, variation, restart, influence of Temperature, etc.). The most well-known of these sets the Daily rate average between –4 and +6 seconds per Day.

WHAT ARE THE ADVANTAGES OF THE ISO 3159 STANDARD?

1. Guaranteed accuracy: watches tested according to the standard meet strict criteria, ensuring the reliability of Time measurements.
2. International harmonization: by applying an identical protocol worldwide, the standard facilitates the comparison and recognition of chronometric performance.
3. Continuous improvement: the definition of measurable thresholds pushes manufacturers to continually optimize the quality and consistency of their Movements.
4. Official recognition: watches compliant with the ISO 3159 standard can be subject to independent, internationally recognized certification.

WHAT ARE THE CERTIFICATION BODIES?

In Switzerland, two institutions are authorized to issue chronometry certificates according to the ISO 3159 standard:

• • the Geneva Chronometry Observatory, managed by the Timelab Foundation
• • the Official Swiss Chronometer Testing Institute (COSC)