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|Unit system||typographic unit|
|1 point in ...||... is equal to ...|
|typographic units||12 points|
|imperial/US units||1/ in|
|metric (SI) units||4.2333 mm|
The pica is a typographic unit of measure corresponding to approximate 1⁄72 of a foot, or 1⁄6 of an inch. Actually a new english Pica was in 1886  defined as .1660 of an inch. Actually this measure was based on the meter: 166 Nonparel equals 35 centimeters.
The pica contains 12 point units of measure. .1660 inch.
The first point-system was designed in 1737 by Pierre Simon Fournier le Jeune (1712–1768). The basis was the Paris foot. 1 foot = 12 thumbs, 1 thumb = 12 stripes, 1 stripe = 6 points.
Around 1780 François-Ambroise "L'éclat" Didot (1730–1804) changed the typographic measures system. Now the larger French Kings Foot was taken as the basis. 12 point Didot equals .1776 inch.
The traditional names for the sizes like cicéro, Petit-Roman, and Gros-Text were replaced by "ten-point", "twelve-point", etc. From that time all work printer before the French Court or French Government had to be printed in this new measurements. As a result this system was accepted more and more. Until the end of commercial letterpress, around 1970 there were still printers using the old Fournier sizes. Monotype moulds Fournier-sized were also available. Because 12 point Fourniers equals 11 point Didot the Fournier-system was wrongly referred as the "Median-system".
The old English Pica was defined as .1667". Monotype made wedges based on both Pica-systems, On the European continent the wedges were based on the old-Pica, and the wedges are marked with an extra E. The tables in English manuals differ subsequently from the tables you find in the French, German, Dutch manuals.
To date, in printing these three pica measures are used:
- The French pica of 12 Didot points (also called cicéro) generally is: 12 × 0.376 = 4.512 mm (0.1776 in).
- The American pica measure of 0.013837 ft. (1⁄72.27 ft). Thus, a pica is 0.166044 in. (4.2175 mm)
- The contemporary computer pica is 1⁄72 of the International foot of 1959, i.e. 4.233 mm or 0.166 in.
Note that these definitions are different from a typewriter's pica setting, which denotes a type size of ten characters per horizontal inch.
Usually, pica measurements are represented with an upper-case "P" with an upper-right-to-lower-left virgule (slash) starting in the upper right portion of the "P" and ending at the lower left of the upright portion of the "P"; essentially drawing a virgule ( / ) through a "P". (P̸) Likewise, points are represented with number of points before a lower-case "p", for example, 5p represents "5 points", and 6P̸2p represents "6 picas and 2 points", and 1P̸1 represents "13 points", which is converted to a mixed fraction of 1 pica and 1 point.
Publishing applications such as Adobe InDesign and QuarkXPress represent pica measurements with whole-number picas left of a lower-case "p", followed by the points number, for example: 5p6, represents 5 picas and 6 points, or 5½ picas.
- L.Ronner: Van leerling tot Zetter, 1914, Amsterdam, NV Drukkerij De Nieuwe Tijd
- "Syntax and basic data types". W3.org. Retrieved 2013-09-21.