Ligne
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The ligne (Template:IPA), or line or Paris line,<ref>Template:Cite journal</ref> is a historic unit of length used in France and elsewhere prior to the adoption of the metric system in the late 18th century, and used in various sciences after that time.<ref>Template:Cite book</ref><ref>Template:Cite journal</ref> The loi du 19 frimaire an VIII (Law of 10 December 1799) states that one metre is equal to exactly 443.296 French lines.<ref name="Débarbat">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
It is vestigially retained today by French and Swiss watchmakers to measure the size of watch casings,<ref name=Swiss>Template:Citation</ref>Template:Efn in button making and in ribbon manufacture.
Current use
Watchmaking
There are 12 lignes to one French inch (pouce). The standardized conversion for a ligne is 2.2558291 mm (1 mm = 0.443296 ligne),<ref name=Débarbat /> and it is abbreviated with the letter L or represented by the triple prime, Template:Char.<ref name=Swiss /> One ligne is the equivalent of 0.0888 international inch.
This is comparable in size to the British measurement called "line" (one-twelfth of an English inch), used prior to 1824.<ref>Oxford English Dictionary</ref> (The French inch at that time was slightly larger than the English one, but the system of 12 inches to a foot and 12 lines to an inch was the same in both cases.)
Hatmaking
Ligne is used in measuring the width of ribbons in men's hat bands,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> at 11.26 per international inch.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Button making
The button trade uses the term ligne (sometimes "line"), but with a substantially different definition: Template:Convert.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite book</ref>