Typometer

The idea of organising type sizes according to a particular point system first appeared during the 18th century, in the 1723 book La Science pratique de l'imprimerie, written by French printer and bookseller Martin-Dominique Fertel.[5] In 1737, French engraver and typecaster Pierre-Simon Fournier (called Fournier the young) invented a tool in the shape of a square that he called prototype,[6] which allowed him to accurately measure type sizes. He also stablished the Fournier point, that could be used for the first time to set a correlation between a type size and a constant number of points. According to his own words,

Pour faire la combinaison des corps, il suffit de savoir le nombre de points typographiques dont ils sont composés. Il faut pour cela que les points ou grandeurs données soient invariables, de manière qu'il puissent servir de guides dans l'imprimerie, comme le pied de roi, les pouces et les lignes en servent dans la géométrie.

In order to combine type sizes, one only needs to know the number of typographic points that compose them. For that, it's important that the points or measures that are given remain constant, so they can be used as guides in the printing press, in the same way that the king's foot, the thumbs and the lines are used in geometry.

— Pierre-Simon Fournier.[6]

This way, in his Table des proportions (proportions table) published in 1737, Fournier the young proposed a scale consisting in 144 typographic points on which he distributed the type sizes that were commonly used in the printing press, which ranged from the Parisienne (the smallest size, which the exception of the Perle, which was rarely used) to the Grosse nonpareille (Great nonpareil, the largest size).[7]

However, Fournier's prototype presented a major disadvantage, because its system of measures was very difficult to compare with the royal inches (pouces de roi) that were commonly used in France at the time. For this reason, French printer François-Ambroise Didot (1730–1804) created a simplified system, which he called typometer,[8] and that he based on the pied du roi.[7][9] This invention was first described in the book Essai de fables nouvelles, by Pierre Didot, François-Ambroise's son.[10]

Didot's new measuring scale was divided in 288 typographic points, instead of the former 144, and described 12 type sizes, instead of the 20 or 22 listed by Fournier the young. As many of the sizes kept their names, but changed their dimensions, a great confusion ensued among printers, and some of them campaigned for a return to the older system.[7] Nevertheless, the Didot points were progressively adopted until becoming the norm. This way of measuring type based in the mediaeval royal units prevailed even after the French Revolution, when the metric system was adopted by France.

In Germany, the French typographic point system was never properly implemented, which resulted in a wide variability of dimensions for type metal. In order to try to solve this situation, in 1879, German and Prussian printer and businessman Hermann Berthold proposed his own system to standardise typographic points based on the metric system.[11] For that purpose, he divided a meter into 2660 identical typographic points. This measure, which is 0,0076 % wider than the Didot point, became the current reference for printing. From 1897 on, German manufacturer A. W. Faber started commercialising sliding rulers that allowed typographers to calculate in a simple manner the measures of their layouts.

• Typographic unit