Point (typography)
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In typography, a point is the smallest unit of measure, it being the subdivision of the pica. It is commonly abbreviated as pt. The traditional printer's point from the era of hot metal typesetting and presswork varied between 0.18 and 0.4 mm depending on various definitions of the foot.
Today, the traditional point has been supplanted by the desktop publishing point (also called the PostScript point), which has been rounded to an even 72 points to the inch (0.3527 mm). In either system, there are 12 points to the pica.
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[edit] The French printer's points
Foreword concerning the conversion from the old French Royal units to the decimal SI unit of length:
The French law for the definitive metre of 1799 states that one decimal meter is exactly 443.296 French lines, or 3 French feet, 0 French inches and 11.296 French lines. The French Royal foot is exactly 9000/27706 metres, or about 0.324839385 m. This conversion value is used below.
[edit] Truchet's point
The clergyman Sébastien Truchet (1657-1729) was the inventor of the modern typographic point in France.
His typographical point measured 1/ 1728 Pied du Roi exactly one, i.e. 15 625 / 83 118 ≤ 0.187 985 755 2 mm.
[edit] Fournier's point
Pierre Simon Fournier (1712-1768) used a typographic point of about 11 / 864 French Royal inch ≈ 0.345 mm. Fournier's point did not achieve lasting popularity.
[edit] Didot's point
- François-Ambroise Didot (1730-1801) retook the idea of Truchet, but defined his typographic point twice as large.
Therefore, the point Didot is 1/ 864 Pied du Roi exactly one, i.e. 15 625 / 41 559 ≤ 0.375 971 510 4 mm
This odd value – due to the divisor 41 559 (prime factors: 3 x 7 x 1979) – was not very flexible for use by typesetters and printers:
So, some printers practiced their own conventional "old French feet":
- 324.920 160 mm, with a point of 0.376 065 mm, i.e. + 0.0249 %. Traditional value in European printers' offices.
- 324.864 000 mm, with a point of 0.376 000 mm, i.e. + 0.0076 %. Used by Hermann Berthold (1831–1904) and many others.
- 324.812 030 mm, with a point of 0.375 940 mm, i.e. – 0.0084 %. Jan Tschichold (1902-1974) states: 266 points in 100 mm.
Or even, according to a proposal of the year 1975, but never applied:
- 324.000 000 mm, with a point of 0.375 000 mm, i.e. – 0.2584 %. Promoted by some, but inaccurate, quite another measure.
Note, that the French National Print Office adopted a point of 0.4 mm exactly and continues to use it today.
The Didot point has been replaced by the DTP point in France and throughout the world.
[edit] The traditional American point system
By the (Kasson) Metric Act (1866), Public Law 39-183, the U.S. Survey foot is 1200/3937 m.
However, this is only 0.0002 % more than the anglo-saxon compromise foot (1959) used below.
- Nelson C. Hawks, in 1879, used a printer's foot of an anglo-saxon foot decreased by 0.3750 %. Therefore the traditional ratio 7200 : 7227 (shortened 800 : 803).
This means that the Hawks' point was 0.013 837 inch or about 0.351 46 mm.
- A second definition proposed: There are exactly 996 printer's points in 350 mm.
This means that this printer's point was 0.013 848 867 inch or about 0.351 405 622 mm.
- Finally, Johnson stated in a third definition, that the printer's foot should be 249 / 250 (anglo-saxon) foot.
This means that the Johnson's typographical point – the later approved one – is: 0.01383 inch and converted by the 1959 value: 0.35136 mm.
In 1886, the Fifteenth Meeting of the Type Founders Association of the United States approved the so-called "Johnson pica" be adopted as the official standard.
This makes the traditional American printer's foot measure 11.952 inches or 303.5808 mm exactly (approxmately 1/72.27 of an inch), at last by respecting the conversion values of 1959 and not the values of 1886.
Just like the French Didot point, the traditional American printer's point was replaced in the 1980s by the current computer DTP point system.
[edit] Current DTP point system
The desk-top publishing point (DTP point) is defined as 1/72 of the anglo-saxon compromise inch of 1959 (25.4 mm), it is approximately 0.0139 inch or 0.3528 mm. Twelve points make up a pica, and six picas make an inch.
The point is the standard unit for measuring font size and leading and other minute items on a printed page. This system was notably promoted by John Warnock and Charles Geschke, the inventors of Adobe PostScript, and it is therefore it is sometimes also called PostScript point.
In metal type, the point size of the font described the size (height) of the metal body on which the typeface's characters were cast. In digital type, the body is now an imaginary design space, but is used as the basis from which the type is scaled (see em).
A measurement in picas is usually represented by placing a lower case p after the number, such as "10p" means "10 picas". Points are represented by placing the number of points after the p, such as 0p5 for "5 points," 6p2 for "6 picas and 2 points", or 1p1 for "13 points" which is converted to a mixed fraction of 1 pica and 1 point. (An alternate nomenclature is described in the pica article.)
