Talk:Pica (typography)

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Article is wrong[edit]

There are more than 152 points in an inch, and 6 picas do not equal an inch. The metric equivalents are therefore off as well. You can look at any "pica pole," a form of ruler that most frequently displays both inches and picas with half-pica (6-point) increments also marked, the difference is quite noticeable at 12 inches, nearly 6 extra points. You can also check Webster's Unabridged (3rd ed.), where the pica is defined as "about 1/6 inch." See also OnlineConversion.com (1 inch equals 72.571428571 points, not 72 points even).

The misinformation in the article flows from a decision made by the designers of PostScript to ignore an established standard. PostScript does away with the small change and treats an inch as containing 72 points. The information is accurate only for PostScript-based typography systems. E.g., the TeX-based typesetting programs use 72.270000003 points to the inch. Ibid. There is also an obsoleted "Didot" point system that was widely used in Europe until the metric system gained ascendancy. "Pica" is also used as a unit of measure on typewriters, where it indicates a typeface with 10 characters per horizontal inch. That is in contrast to "elite" typewriter spacing which is 12 characters per inch.

The idea that 6 picas or 72 points equals an inch is either a mere approximation or specific to Postscript (your choice), not an accurate calculation based on the standard, except in the PostScript world. (I note that the article's final paragraph on markup conventions is PostScript-specific; it assuredly is not the markup used historically in the printing industry.) Anyone who has composed large pages in hot type (e.g., newspaper pages) knows that the approximation becomes more and more useless as the dimension of the composition area increases. That is why typographers do/did their calculations in picas and points rather than inches. Unfortunately, the misinformation has propagated across the Net. (Try Google for "picas per inch," a powerful testament to the power of historical revisionism by the computer industry.)

You can find an overview of the point's (and pica's) generally accepted history at this site. But see Father Truchet, the typographic point, Romain du roi, and tilings (PDF) (arguing that Truchet rather than Fournier should be credited with creating the point).

I note that the misinformation is spreading on Wikipedia. See WYSIWYG ("72 PPI came from the standard of 72 'points' per inch used in the commercial printing industry").

This is important; we are discussing a standard that was unchanged for more than a hundred years until PostScript came along.

Someone with time needs to research and rewrite this article

-Marbux

I haven't written the detailed history that's needed, but I've corrected the factual inaccuracy and mentioned PostScript. Maybe the article could be retagged for expansion. Regarding the "pica" on typewriters: IMO it is plausible that a typewriter font at 10 characters/inch might have a line height of one pica. Seahen 16:05, 19 February 2006 (UTC)
"When Adobe created the PostScript standard..." would be much more appropriate than "A corporation proposing the PostScript standard..."

SI units?[edit]

Can anyone substitute or at least add the corresponding values in SI units? --Mecanismo 18:06, 9 October 2005 (UTC)

Wouldn't make much sense to substitute, since the pica is defined as being a sixth of an inch, but I've added the approximate millimeter equivalent. Factitious 20:05, 10 October 2005 (UTC)

abbreviation[edit]

Cascading Style Sheets use 'pc' for the abbreviation for pica. Jim albright (talk) 18:01