“
The measure or length to which the type lines are set should be related to the size of the type. A ready method of deciding a suitable measure to which any given type should be set is to calculate it from the length of the complete lowercase
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
alphabet, which is known as the a-z length. As a wide letter may be set to a longer length and vice versa, this method assures that the measure is related to the set of the type face. A satisfactory limit may be set by using the alphabet as a minimum and three alphabet widths as a maximum. The maximum measure would allow an average of about twelve words to the line.
— Setting the measure. How to Plan Print, J C Tarr, 1938, Crosby, Lockwood and Sons, London.
