Typographic unit

Typographic units are the units of measurement used in typography or typesetting. Traditional typometry units are different from familiar metric units because they were established in the early days of printing. Though most printing is digital now, the old terms and units have persisted. Even though these units are all very small, across a line of print they add up quickly. Confusions such as resetting text originally in type of one unit in type of another will result in words moving from one line to the next, resulting in all sorts of typesetting errors (viz. rivers, widows and orphans, disrupted tables, and misplaced captions). Before the popularization of desktop publishing, type measurements were done with a tool called a typometer.

Development

In Europe, the Didot point system was created by François-Ambroise Didot (1730–1804) in c. 1783. Didot's system was based on the 1742 standard established for the Kingdom of France by Pierre Simon Fournier, but Didot modified Fournier's system by adjusting the base unit to a French Royal inch (pouce), whereas Fournier's unit was based on the traditional Paris inch. However, the basic idea of the point system – to generate different type sizes by multiplying a single minimum unit calculated by dividing a base measurement unit such as one French Royal inch – was not Didot's invention, but Fournier's. In Fournier's system, an approximate French Royal inch (pouce) is divided by 12 to calculate 1 ligne, which is then divided by 6 to get 1 point. Didot just made the base unit (one French Royal inch) identical to the standard value defined by the government. In Didot's point system:

1 point = 1⁄6 ligne = 1⁄72 French Royal inch = 15 625⁄41 559 mm ≤ 0.375 971 510 4 mm, however in practice mostly: 0.376 mm (i.e. + 0.0076%). Both in Didot's and Fournier's systems, some point sizes have traditional names such as Cicero (before introduction of point systems, type sizes were called by names such as Cicero, Pica, Ruby, Great Primer, etc.).

1 cicero = 12 Didot points = 1⁄6 French Royal inch = 62 500⁄13 853 mm ≤ 4.511 658 124 6 mm, also in practice mostly: 4.512 mm (i.e. + 0.0076%). The Didot point system has been widely used in European countries. An abbreviation for it that these countries use is "dd", employing an old method for indicating plurals. Hence "12 dd" means twelve didot points. In Britain and the United States, many proposals for type size standardization had been made by the end of the 19th century (such as Bruce Typefoundry's mathematical system that was based on a precise geometric progression). However, no nationwide standard was created until the American Point System was decided in 1886. The American Point System was proposed by Nelson C. Hawks of Marder Luse & Company in Chicago in the 1870s, and his point system used the same method of size division as Fournier's; viz. dividing 1 inch by six to get one pica, and dividing it again by 12 to get one point. However, the American Point System standardized finally in 1886 is different from Hawks's original idea in that one pica is not precisely equal to 1⁄6 inch (neither the Imperial inch nor the US inch), as the United States Type Founders' Association defined the standard pica to be the Johnson Pica, which had been adopted and used by Mackellar, Smiths and Jordan type foundry (MS&J), Philadelphia. As MS&J was very influential in those days, many other type foundries were using the Johnson Pica. Also, MS&J defined that 83 Picas are equal to 35 centimeters. The choice of the metric unit for the prototype was because at the time the Imperial and US inches differed in size slightly, and neither country could legally specify a unit of the other. The Johnson Pica was named after Lawrence Johnson who had succeeded Binny & Ronaldson in 1833. Binny & Ronaldson was one of the oldest type foundries in the United States, established in Philadelphia in 1796. Binny & Ronaldson had bought the type founding equipment of Benjamin Franklin's (1706–1790) type foundry established in 1786 and run by his grandson Benjamin Franklin Bache (1769–1798). The equipment is thought to be that which Benjamin Franklin purchased from Pierre Simon Fournier when he visited France for diplomatic purposes (1776–85). The official US standard approved by the Fifteenth Meeting of the Type Founders Association of the United States in 1886 was this Johnson pica, equal to exactly 0.166 inch. Monotype wedges used in England and America were based on a pica = 0.1660 inch. But on the European continent all available wedges were based on the "old-pica" 1 pica - .1667 inch. These wedges were marked with an extra E behind the numbers of the wedge and the set. These differences can also be found in the tables of the manuals. In the American point system:

1 Johnson pica = exactly 0.166 inch (versus 0.166 = 1⁄6 inch for the DTP-pica) = 4.2164 mm. 1 point = 1⁄12 pica = exactly 0.013 83 inch = 0.351 36 mm. The American point system has been used in the US, Britain, Japan, and many other countries. Today, digital printing and display devices and page layout software use a unit that is different from these traditional typographic units. On many digital printing systems (desktop publishing systems in particular), the following equations are applicable (with exceptions, most notably the popular TeX typesetting system and its derivatives).

1 pica = 1⁄6 inch (British/American inch of today) = 127⁄30 mm = 4.23 mm. 1 point = 1⁄12 pica = 1⁄72 inch = 127⁄360 mm = 0.3527 mm. Digital displays and printing led to the use an additional unit:

1 twip = 1⁄20 point = 1⁄1440 inch = 127⁄7200 mm = 0.017 638 mm. Fournier's original method of division is now restored in today's digital typography. Comparing a piece of type in didots for Continental European countries – 12 dd, for example – to a piece of type for an English-speaking country – 12 pt – shows that the main body of a character is actually about the same size. The difference is that the languages of the former often need extra space atop the capital letters for accent marks (e.g. Ñ, Â, Ö, É), but English rarely needs this.

Metric units

… excerpt ends here. Continue reading the full article.