Didot Point

In typography, the point is the smallest unit of measure. It is used for measuring font size, leading, and other items on a printed page. The size of the point has varied throughout printing's history. Since the 18th century, the size of a point has been between 0.18 and 0.4  millimeters. Following the advent of desktop publishing in the 1980s and 1990s, digital printing has largely supplanted the letterpress printing and has established the DTP point (DeskTop Publishing point) as the ''de facto'' standard. The DTP point is defined as of an international inch () and, as with earlier American point sizes, is considered to be of a pica.

In metal type, the point size of the font describes the height of the metal body on which the typeface's characters were cast. In digital type, letters of a font are designed around an imaginary space called an '' em square''. When a point size of a font is specified, the font is scaled so that its em square has a side length of that particular length in points. Although the letters of a font usually fit within the font's em square, there is not necessarily any size relationship between the two, so the point size does not necessarily correspond to any measurement of the size of the letters on the printed page.

History

The point was first established by the Milanese typographer, Francesco Torniella da Novara ( – 1589) in his 1517 alphabet, ''L'Alfabeto''. The construction of the alphabet is the first based on logical measurement called "Punto," which corresponds to the ninth part of the height of the letters or the thickness of the principal stroke.

Notations

A measurement in points can be represented in three different ways. For example, 14 points (1 pica plus 2 points) can be written:

* (12 points would be just "")—traditional style
* 1p2 (12 points would be just "1p")—format for desktop
* 14pt (12 points would be "12pt" or "1pc" since it is the same as 1 pica)—format used by Cascading Style Sheets defined by the World Wide Web Consortium.

Varying standards

There have been many definitions of a "point" since the advent of typography. Traditional continental European points at about are usually a bit larger than English points at around .

French points

The Truchet point, the first modern typographic point, was of a French inch or of the royal foot. It was invented by the French clergyman Sébastien Truchet. During the metrication of France amid its revolution, a 1799 law declared the meter to be exactly 443.296 French lines long. This established a length to the royal foot of  m or about 325 mm, which made the Truchet point equal to  mm or about . It has also been cited as exactly 0.188 mm.

The Fournier point was established by Pierre Simon Fournier in 1737. The system of Fournier was based on a different French foot of c. 298 mm. With the usual convention that 1 foot equals 12 inches, 1 inch (''pouce'') was divided into 12 lines (''lignes'') and 1 line was further divided into 6 typographic points (''points typographiques''). 1 point Fournier = 0.0135 English inches.

Fournier printed a reference scale of 144 points over two inches; however, it was too rough to accurately measure a single point.

The Didot point, established by François-Ambroise Didot in 1783, was an attempt to improve the Fournier system. He did not change the subdivisions (1 inch = 12 subdivisions = 72 points), but defined it strictly in terms of the royal foot, a legal length measure in France: the Didot point is exactly of a French foot or of a French inch, that is (by 1799)  mm or about . Accordingly, one Didot point is exactly two Truchet points.

However, 12 Fournier points turned out to be 11 Didot points, giving a Fournier point of about ; later sources state it as being . In Belgium the Fournier system was used until the 1970s and later. It was called the "mediaan"-system. To avoid confusion between the new and the old sizes, Didot also rejected the traditional names, thus ''parisienne'' became ''corps'' 5, ''nonpareille'' became ''corps'' 6, and so on. The Didot system prevailed because the French government demanded printing in Didot measurements.

The Fournier point did not achieve lasting popularity despite being revived by the Monotype Corporation in 1927. It was still a standard in Belgium, in parts of Austria, and in Northern France at the beginning of the 20th century.

Other European points

Approximations were subsequently employed, largely owing to the Didot point's unwieldy conversion to metric units (the divisor of its conversion ratio has the prime factorization of ).

In 1878, Hermann Berthold defined 798 points as being equal to 30 cm, or 2660 points equalling 1 meter: that gives around to the point. A more precise number, , sometimes is given; this is used by TeX as the unit. This has become the standard in Germany and Central and Eastern Europe. This size is still mentioned in the technical regulations of the Eurasian Economic Union.

Metric points

pdfTEX, but not plain TeX or LaTeX, also supports a ''new Didot point'' (''nd'') at  mm or and refers to a not further specified 1978 redefinition for it.

The French National Print Office adopted a point of  mm or in about 1810 and continues to use this measurement today (though "recalibrated" to ).

JapaneseJIS X 4052:2000, JIS Z 8125:2004 and German standardization bodies instead opted for a metric typographic base measure of exactly  mm or , which is sometimes referred to as the ''quart'' in Japan. The symbol ''Q'' is used in Japanese after the initial letter of ''quarter millimeter''. Due to demand by Japanese typesetters, CSS adopted ''Q'' in 2015.

ISO 128 specifies preferred line thicknesses for technical drawings and ISO 9175 specifies respective pens. The steps between nominal sizes are based on a factor of √2 ≈ 1.414 in order to match ISO 216 paper sizes. Since the set of sizes includes thicknesses of 0.1 mm, 0.5 mm, 1 mm and 2 mm, there is also one of 0.35 mm which is almost exactly 1 pica point. In other words, 2^−1.5 mm = mm approximates an English typographic point rather well.

American points

The basic unit of measurements in American typography was the pica, usually approximated as one sixth of an inch, but the exact size was not standardized, and various type foundries had been using their own.

After the American war of Independence Benjamin Franklin was sent as commissioner (Ambassador) for the United States to France (December 1776 to 1785). While living there he had intimate contact with the Fournier family, including the father and Pierre Simon Fournier. Franklin wanted to teach his grandson Benjamin Franklin Bache about printing and typefounding, and arranged for him to be trained by Francois Ambroise Didot. Franklin then imported French typefounding equipment to Philadelphia to help Bache set up a type-foundry. Around 1790, Bache published a specimen sheet with some Fournier types. After the death of Franklin, the matrices and the Fournier mould were acquired by Binny and Ronaldson, the first permanent type-foundry in America. Successive mergers and acquisitions in 1833, 1860 and 1897 saw the company eventually become known as MacKellar, Smith & Jordan. The Fournier cicero mould was used by them to cast pica-sized type.

Nelson Hawks proposed, like Fournier, to divide one American inch exactly into six picas, and one pica into 12 points. However, this saw an opposition because the majority of foundries had been using picas less than one sixth of an inch. So in 1886, after some examination of various picas, the Type Founders Association of the United States approved the pica of the L. Johnson & Co. foundry of Philadelphia (hence the Johnson pica) as the most established. The company went on to become MacKellar, Smiths, & Jordan Co. and was finally acquired by the Type Founders Association. The official definition of one pica is , and one point is . That means 6 picas or 72 points constitute standard inches. A less precise definition is one pica equals , and one point . It was also noticed that 83 picas is nearly equal to 35 cm, so the Type Founders Association also suggested using a 35 cm metal rod for measurements, but this was not accepted by every foundry.

This has become known as the American point system. The British foundries accepted this in 1898.

In modern times this size of the point has been approximated as exactly () of the inch by Donald Knuth for the default unit of his TeX computer typesetting system and is thus sometimes known as the , which is 0. mm.

Old English points

Although the English Monotype manuals used 1 pica = .1660 inch, the manuals used on the European continent use another definition: there 1 pica = .1667 inch, the Old English pica.

As a consequence all the tables of measurements in the German, Dutch, French, Polish and all other manuals elsewhere on the European continent for the composition caster and the super-caster are different in quite some details.

The Monotype wedges used at the European continent are marked with an extra E behind the set-size: for instance: 5-12E, 1331-15E etc. When working with the E-wedges in the larger sizes the differences will increase even more.

Desktop publishing point

The desktop publishing point (DTP point) or PostScript point is defined as or 0.013 of the international inch, making it equivalent to  mm = 0.352 mm. Twelve points make up a pica, and six picas make an inch.

This specification was developed by John Warnock and Charles Geschke when they created Adobe PostScript. It was adopted by Apple Computer as the standard for the display resolution of the original Macintosh desktop computer and the print resolution for the LaserWriter printer.

In 1996, it was adopted by W3C for Cascading Stylesheets (CSS) where it was later related at a fixed 3:4 ratio to the pixel due to a general (but wrong) assumption of 96 pixel-per-inch screens.

Apple point

Since the advent of high-density "Retina" screens with a much higher resolution than the original 72 dots per inch, Apple's programming environment Xcode sizes GUI elements in ''points'' that are scaled automatically to a whole number of physical pixels in order to accommodate for screen size, pixel density and typical viewing distance. This ''Cocoa point'' is equivalent to the ''pixel'' px unit in CSS, the ''density-independent pixel'' dp on Android and the ''effective pixel'' epx or ep in Windows UWP.

Font sizes

In lead typecasting, most font sizes commonly used in printing have conventional names that differ by country, language and the type of points used.

Desktop publishing software and word processors intended for office and personal use often have a list of suggested font sizes in their user interface, but they are not named and usually an arbitrary value can be entered manually. Microsoft Word, for instance, suggests every even size between 8 and 28 points and, additionally, 9, 11, 36, 48 and 72 points, i.e. the larger sizes equal 3, 4 and 6 picas. While most software nowadays defaults to DTP points, many allow other units, especially code-based systems like TeX and CSS.

See also

* Pica (typography)
* Body height (typography)

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