Movement sizes are still given in lignes: Seiko's 1913 Laurel is described by its own museum as having a 12-ligne movement. The unit descends from the French pouce, or Paris inch, of the pre-metric system, a ligne being one twelfth of one.
The problem. A metric value for the ligne is quoted on a great many websites, usually as 2.255, 2.256 or 2.2558 mm. Every one of those sources is of a kind this Codex does not cite: encyclopedias, dealer pages, enthusiast editorial and conversion charts. The only compiled glossary located that states a value is hosted by a horological association but was written by an auction house, which the source policy also excludes.
So no figure is published here. Three different values circulate at three-decimal precision; adopting one on the strength of uncitable sources would be exactly the failure this Codex exists to avoid.
How it gets resolved. The pouce derives from the pied du roi, which is documented in metrology history. A national metrology body or a university-press history of metrication would let the value be derived and stated properly. Until then the entry stands as a question.
Sources
Every statement above traces to one of these. Read on the date shown.
- Tier 1 The Seiko Museum Ginza, "Japan's First Wristwatch, Laurel", records a "12 ligne movement", establishing the unit's use without defining it, source read 2026-09-26