Four types

The timepieces suitable for submission for the title of chronometer are listed according to four types.

Mechanical instruments (with balance spring oscillator)

• Type I: wristwatches
• Type II: Pocket watches (Lépine or Savonette)
• Type III: Fixed time devices (carriage clocks, desk clocks, etc.).

Quartz instruments

• Type IV: Wrist watches with quartz oscillator

Type I (balance spring oscillator) represents the overwhelming majority of instruments that the COSC tests. Its certification refers to the ISO 3159 standard. The certifications of the other three types are defined by the COSC, as there is no international standard for them.