ISO 3159:2009

Overview

ISO 3159:2009 - Timekeeping instruments - Wrist-chronometers with spring balance oscillator defines what constitutes a mechanical wrist chronometer and specifies the test programme and minimum acceptance criteria for certification. Published by ISO/TC 114 (Horology) as the second edition (2009), the standard replaces the 1976 edition and sets objective limits for precision wristwatches regulated by a spring-balance (balance-spring) oscillator. (Wristwatches using a tuning-fork oscillator are currently subjected to these tests pending separate standards.)

Key topics and technical requirements

• Definition: A chronometer is a precision wristwatch regulated for different positions and conditions of use; certification is issued by a neutral authority when minimum requirements are met.
• Categories: Two casing-size categories based on casing diameter or casing-up surface:
  • Category 1: > 20 mm (or > 314 mm² surface)
  • Category 2: ≤ 20 mm (or ≤ 314 mm² surface)
• Test programme: A 15-day sequence of positional and temperature tests (baseline at 23 °C with additional checks at 8 °C and 38 °C). Positions (symbolized per ISO 3158) include 6H, 3H, 9H, FH, CH and specified observation days; auxiliary functions are generally inactive except where noted.
• Measured criteria (defined mathematically in the standard):
  • Mean daily rate (M)
  • Mean variation in rates (V)
  • Greatest variation in rates (Vmax)
  • Difference between horizontal and vertical positions (D)
  • Greatest deviation in rates (P)
  • Temperature variation in rate (C)
  • Resumption of the rate after tests (R)
• Minimum acceptance limits (examples from standard):
  • Mean daily rate M: Category 1 = −4 to +6 s/d; Category 2 = −5 to +8 s/d
  • Mean variation V: Category 1 = 2 s/d; Category 2 = 3.4 s/d
  • Greatest variation Vmax: Category 1 = 5 s/d; Category 2 = 7 s/d
  • D (horizontal vs vertical): Cat 1 = −6 to +8 s/d; Cat 2 = −8 to +10 s/d
  • P (greatest deviation): Cat 1 = 10 s/d; Cat 2 = 15 s/d
  • Temperature dependence C: Cat 1 = ±0.6 s/(d·°C); Cat 2 = ±0.7 s/(d·°C)
  • Resumption R: Cat 1 = ±5 s/d; Cat 2 = ±6 s/d
• Normative reference: ISO 3158 for symbolization of control positions.

Applications and users

• Watch manufacturers and movement designers use ISO 3159 for product development, quality control and to design movements that meet chronometer certification.
• Testing laboratories and official certifying authorities (chronometer institutes) apply the test programme and acceptance limits to issue certificates.
• Retailers and consumers use the certification to verify precision and performance claims.
• R&D teams use the criteria to compare materials, escapement designs and regulation methods for precision wristwatches.

Related standards

• ISO 3158 - Symbolization of control positions (normative reference cited by ISO 3159)
• Produced under ISO/TC 114 (Horology), ISO 3159 is the authoritative reference for mechanical wrist-chronometer testing and certification.

Keywords: ISO 3159, chronometer, wrist-chronometer, timekeeping instruments, spring balance oscillator, precision wristwatch testing, chronometer certification.