conte du pourquoi (11. 178)

Generally in the International System of Units, as Futility Closet informs, the abbreviation of metrics are only afforded an uppercase character when the unit of measure is a personal namesake—see also—like the newton, ampere, joule, siemens, volt, hertz and kelvin, but the litre, particularly for jurisdictions with the inheritance of the Imperial System and one still singularly holding-fast, the litre was especially fraught for researchers for its potential to be confused with the digit 1. To avoid this confusion, most scientific and labelling authorities adopted a scripted ℓ as a volumetric symbol, but conventions still held in the US, Canada and Australia. Originally as an April Fools’ Day hoax, Kenneth Woolner of the University of Waterloo created the fictional heir to a sixteenth century wine bottle manufacture concern who purposed an industry standard (famously conventional), Claude Émile Jean-Baptise Litre, to promote the use of an upper-case L. I do hope that Litre had a full, fake biography.  The account was re-printed as fact by an IUPAC journal in 1978 as factual, and though subsequently retracted, the exception is now allowed.