LINE

The line is an old unit of length, inherited from the French measurement system of the Ancien Régime, still commonly used in watchmaking to express the diameter of a Calibre. The so-called “King’s” line or “Paris line,” often denoted by three primes (”’), was equal to one twelfth of an inch and was fixed by the law of 19 Frimaire Year VIII at approximately 2.2558 mm; it should not be confused with the line of the Anglo-Saxon system, which today equals exactly 2.116 mm. Although watchmaking has adopted the millimeter for most of its measurements, the line has survived in technical vocabulary to designate the size of blanks and movements: a Calibre of “11 and a half lines” thus measures approximately 25.9 mm in diameter. This unit allows professionals to easily compare the dimensions of movements and to designate Calibres without systematically resorting to the metric system. It is also found, in a purely traditional way, in other trades, such as the measurement of Cork stoppers in viticulture. Still very much alive in catalogs, technical sheets, and exchanges between specialists, the line testifies to watchmaking’s attachment to its historical measurement conventions.