I quote from a web page that is gone: The point measurement was developed as a standard in the 19th century by Pierre Simon Fournier and F(irmin) Didot. Known as the Didot Point System, 12 points equal one cicero. The British/American version (proposed by Nelson Hawks in 1878) is based on the pica - which is also 12 points, or 4.233 millimetres, but is actually slightly smaller that a Didot Point. The point size is determined by measuring the distance from the ascent line (top of the capitals) to the descent line (bottom-most descender). To confuse matters, many European countries measure type in millimetres (1mm equals 2.85pt).

EXTERNAL LINKS
Google search page

INTERNAL LINKS
Type measurements ⦿ Modern style [Bodoni, Didot, Walbaum, Thorowgood, Computer Modern, etc.] ⦿

Luc Devroye ⦿ School of Computer Science ⦿ McGill University Montreal, Canada H3A 2K6 ⦿ lucdevroye@gmail.com ⦿ http://luc.devroye.org ⦿ http://luc.devroye.org/fonts.html