Editing Typographic unit (section)

== Development ==
In Europe, the Didot point system was created by [[Didot family#François-Ambroise Didot|François-Ambroise Didot]] (1730–1804) in c. 1783. Didot's system was based on [[Pierre Simon Fournier]]'s (1712–1768), but Didot modified Fournier's by adjusting the base unit precisely to a [[Paris inch|French Royal inch (''pouce'')]], as Fournier's unit was based on a less common foot.

[[Image:FournierScale144pts.jpg]]

(Fournier's printed scale of his point system, from ''Manuel Typographique'', Barbou, Paris 1764, enlarged)

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.<ref group="note">
Actually, Sebastien Truchet (1657–1729) had invented a similar type sizing system before Fournier implemented his point system. Truchet's system was applied to the types of the Imprimerie Royale, the ''romains du roi''. It is thought that Fournier knew about Truchet's scheme that was based on the standard French Royal inch and a very fine unit of <sup>1</sup>⁄<sub>204</sub> ''[[ligne]]''. For further information on Truchet's system, refer to James Mosley's "The New Type Bodies of the Imprimerie Royale", pp. 400–408, Vol. 3, ''The Manuel Typographique of Pierre-Simon Fournier'' le jeune, Darmstadt 1995. and Jacques André's "Truchet & Types" [http://jacques-andre.fr/faqtypo/truchet/truchet1E.html].
</ref> 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 (typography)|point]] = <sup>1</sup>⁄<sub>6</sub> ''[[ligne]]'' = <sup>1</sup>⁄<sub>72</sub> [[Paris inch|French Royal inch]] = <sup>15&nbsp;625</sup>⁄<sub>41&nbsp;559</sub>&nbsp;mm <small>≤</small>&nbsp;0.375&nbsp;971&nbsp;510&nbsp;4&nbsp;mm, however in practice mostly: 0.376&nbsp;mm (i.e. + 0.0076%).

Both in Didot's and Fournier's systems, some point sizes have [[Traditional point-size names|traditional names]] such as ''[[Cicero (typography)|Cicero]]'' (before introduction of point systems, type sizes were called by names such as ''Cicero'', ''[[Pica (typography)|Pica]]'', ''[[Agate (typography)|Ruby]]'', ''[[Great primer|Great Primer]]'', etc.).

*1 ''cicero'' = 12 Didot points = <sup>1</sup>⁄<sub>6</sub> French Royal inch = <sup>62&nbsp;500</sup>⁄<sub>13&nbsp;853</sub>&nbsp;mm <small>≤</small>&nbsp;4.511&nbsp;658&nbsp;124&nbsp;6&nbsp;mm, also in practice mostly: 4.512&nbsp;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&nbsp;dd" means twelve didot points.

In Britain and the United States, many proposals for type size standardization had been made by the end of 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, & Co.|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&nbsp;[[inch]] by 6 to get 1 [[Pica (typography)|pica]], and dividing it again by 12 to get 1 point. However, the American Point System standardized finally in 1886 is different from Hawks' original idea in that 1 pica is not precisely equal to <sup>1</sup>⁄<sub>6</sub> [[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.<ref group="note"> Regarding the background of the adoption of the Johnson Pica, Mr. Richard L. Hopkins, author of ''Origin of The American Point System'' says: "The major issue then was the expense involved in re-tooling literally hundreds of molds in each foundry to make them all conform to the new system. If they could avoid just a few sizes being altered, it would save hundreds of thousands of dollars. That is why the MS&J (Johnson) pica was adopted."
</ref> Also, MS&J defined that 83 Picas are equal to 35 centimeters. The choice of the [[metric system|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 (Type-founder)|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 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&nbsp;inch.{{citation needed|date=September 2023}} Therefore, the two other – very close – definitions, 1200&nbsp;/&nbsp;7227&nbsp;inch and 350&nbsp;/&nbsp;83&nbsp;mm, are both unofficial{{citation needed|date=September 2023}}.

Monotype wedges used in England and America were based on a pica = .1660&nbsp;inch. But on the European continent all available wedges were based on the "old-pica" 1 pica - .1667&nbsp;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&nbsp;inch ''(versus 0.16<span style="text-decoration: overline">6</span> = <sup>1</sup>⁄<sub>6</sub>&nbsp;inch for the DTP-pica)'' = 4.2164&nbsp;mm.
*1 point = <sup>1</sup>⁄<sub>12</sub> pica = exactly 0.013&nbsp;8<span style="text-decoration: overline">3</span> inch = 0.351&nbsp;3<span style="text-decoration: overline">6</span>&nbsp;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<ref name=LaTeX/Length>[[Wikibooks:LaTeX/Lengths]]</ref>).

*1 pica = <sup>1</sup>⁄<sub>6</sub>&nbsp;inch (British/American inch of today) = 4.23<span style="text-decoration: overline">3</span>&nbsp;mm.
*1 point = <sup>1</sup>⁄<sub>12</sub> pica = <sup>1</sup>⁄<sub>72</sub> inch = <sup>127</sup>⁄<sub>360</sub>&nbsp;mm = 0.352<span style="text-decoration: overline">7</span>&nbsp;mm.

Digital displays and printing led to the use an additional unit:

*1 [[twip]] = <sup>1</sup>⁄<sub>20</sub> point = <sup>1</sup>⁄<sub>1440</sub> inch = <sup>127</sup>⁄<sub>7200</sub>&nbsp;mm = 0.017&nbsp;63<span style="text-decoration: overline">8</span>&nbsp;mm.

Fournier's original method of division is now restored in today's digital typography.{{citation needed|date=September 2019}}

Comparing a piece of type in didots for Continental European countries – 12&nbsp;dd, for example – to a piece of type for an English-speaking country – 12&nbsp;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.