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THE MONOTYPE-UNIT-SYSTEM

calculations on the unit system

THE PRINCIPAL UNIT SYSTEM Wednesday January 14th, 2004, par John Cornelisse


The Monotype "unit"-system.

The basis for this system is the good old inch and the pica.

1 inch = 1" = 25.4 mm 1 pica = 1/6" = .1667"

Historically the inch has been based on the length of three rye-grains. On the continent we compare the height of our characters with the length of the feet of a old French king if we use the system introduced by Didot.

1 cicero Didot = .1776" 1 point Didot = .0148"

To enhance the possibility to vary the pica is divided into 12 points, and each point into 4 equal parts.

1 pica point = 1/72" = .01389" pica point = 1/288" = .003472"

Each multiple of pica points is called a "set". And each set is divided into 18 units. So we have:

6 set = 6 pica-points = 6 * .01389" = .08333" 1 unit 6 set = .00046296"

6 set= 6 p.points = 6.25 * .01389" = .08680" 1 unit 6 set = .00048225"

6 set= 6 p.points = 6.5 * .01389" = .09028" 1 unit 6 = .00050154"

6 set= 6 p.points = 6.75 * .01389" = .09375" 1 unit 6 set = .00052083"

7 set = 7 p.points = 7 * .01389" = .09722" 1 unit 7 set = .00054012"

....

12 set = 12 pica-point = .1667" 1 unit 12 set = .00925925"

13 set = 13 pica-point = .1806" 1 unit 13 set =.00100308"

14 set = 14 pica-point = .1944" 1 unit 14 set =.01080247"

etc.

The widest character - often the capital ?W? - in a font is called the set of that font. The widths of all characters in the font are made to be multiples of the unit of that set.

So we have character of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 units. Some special chars can even be wider. Up to 23 units.

For calculations we use the "1-set":

1 pica = 1/6 inch = 12 pica points

1 pica point = 1/72" = 18 units

1-set 1 unit 1-set = 1/18 * 1/72 = 1/1296" = .0007716049"

On a mat we find some numbers engraved:

1) The charater indentifier, most times 3 digets

f.i. Garamond roman 156, italic 174, bold 201

2) under it the pointsize in pica points

If a ’D’ is added to the second number the font is produced for continental Europe and adjusted to the Didot system, though all calculations will still be made in the English-pica-unit-system.


Postcriptum


Notes




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