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A point is a unit of measure in typography. It is abbreviated as: pt. It corresponds mostly to 1/ 864 of its respectiv foot. So, there are 12 pt. in the pica and 72 pt. in the inch.
The French printer's points
Forword concerning the conversion from the old French Royal units to the decimal SI unit of length:
The French law for the definitiv metre of 1799 states: one decimal meter is exactly 443.296 French lines = 3 French feet, 0 French inch and 11.296 French lines.
Since the French Royal foot is exactly 9000 / 27 706 metre, i.e. about 0.324 839 385 m. This conversion value is used below.
Truchet's point
The clergyman Sébastien Truchet (1657-1729) was the real 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.
Fournier's point
Pierre Simon Fournier (1712-1768) used a typographical point of about 11 / 864 French Royal inch ≈ 0.345 mm. It was not used later on, anymore.
Didot's point
- François-Ambroise Didot (1730-1801) retook the idea of Truchet, but defined his typographical point twice larger.
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) – did not satisfie many European printers later on:
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 printer's value in the European printer's 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 an other measure.
Note, that the French National Print Office adopted a point of 0.4 mm exactly one and still nowadays continues to use it.
Like anywhere else, the Didot point, as well as in France as in the rest of Europe, is widely replaced by the currently used DTP point.
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 approuved 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, 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 is now – also in the United States of America – widely ousted by the current computer DTP point system.
The current DTP point system
The current DeskTop Publishing point (DTP point) is defined as 1/72 of the anglo-saxon compromise inch of 1959, i.e. 0.0138 inch or 0.3527 mm.
It was notably promoted by Warnock and Geschke, the inventors of Adobe PostScript. Therefore it is sometimes also called PostScript point.
The point is the standard unit for measuring font size and leading and other minute items on a printed page.
Twelve points make up a pica, there are 72 points in an inch. (The actual visible size of 1 inch high text is around 96pt), or 6 picas in an inch, a point is 1/12 of a pica.
A measurement in picas is usually represented by placing a small p after the number of picas. "10 picas" is thus abbreviated 10p. Likewise, points are represented by placing the number of points after a small 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.
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