92. The definitions of the line and point in the text do not correspond to their values in the table; the text is simply wrong! Even when the correct values of six points per line and twelve points per inch are substituted for Diderot’s values, the table makes a perfectly simple concept quite unnecessarily obscure. But Fournier’s admirable tables in his Manuel Typographique make all clear. See note 43.

The scale of two inches’ length is divided into 144 points; one inch is thus 72 points. The body sizes are defined so that each can be made up as a multiple of a smaller body or as the sum of multiples of smaller bodies. For the larger type sizes many such combinations are possible and the centre column lists these, or some of them.

In the rightmost columns the body size of the type named in the leftmost column is expressed as a sum of x Lines + y Points, where a line contains 6 points. Note that the size is given opposite the last line of text in the middle column relevant to that type. It is very easy to read the wrong size by taking the figures from the line below which nearly aligns with the next index size. The key to understanding the table is to convert the Lines + Points sum to points and to use only this number in making comparisons. A few examples may help:

The smallest type, Parisienne has a body of 5 points (0 lines, 5points)

Nompareille is 6 points (1 line, 0 points as expressed in the table)

Cicéro is 12 points (2 lines, 0 points) and is equivalent to (middle column) 2 Nompareilles ( 2 x 6) OR 1Parisienne + 1 Mignone (5 + 7)

And so on with the number of possible combinations increasing with increasing type sizes.

Anyone who wishes to do calculations with this system would be well advised to ignore Diderot’s table and to work from Fournier’s tables which simply express the size of each body in points. The relationships between the type sizes are then transparent. According to his own account Fournier invented the points system in 1737; in fact, Truchet had proposed a (different) points system earlier. Fournier did an enormous service to typography though his point size was later modified by basing it on the inch of the Pied de Roi - the official French foot - rather than on Fournier’s inch. The point varied in size in different countries at different times though it was always approximately 1/72 of an Imperial inch. The point has now been standardized as the DTP (desktop publishing) point with 1 point = exactly 1/72 inch in British and US units, and this is now the standard measure for type size.