The memoir class - The UK TeX Archive

UNITS OF MEASUREMENTxxxviiThe point system was invented by Pierre Fournier le jeune in 1737 with a length of0.349mm. Later in the same century François-Ambroise Didot introduced his point systemwith a length of 0.3759mm. This is the value still used in Europe. Much later, in 1886,the American Type Founders Association settled on 0.013837in as the standard size for thepoint, and the British followed in 1898. Conveniently for those who are not entirely metricin their thinking this means that six picas are approximately equal to one inch.The big point is somewhat of an anomaly in that it is a recent invention. It tends tobe used in page markup languages, like PostScript 5 , in order to make calculations quickerand easier.The above units are all constant in value. There are also some units whose value dependson the particular font being used. The em is the nominal height of the current font;it is used as a width measure. An en is half an em. The ex is nominally the height of theletter ‘x’ in the current font. You may also come across the term quad, often as in a phraselike ‘starts with a quad space’. It is a length defined in terms of an em, often a quad is 1em.5 PostScript is a registered trademark of Adobe Systems Incorporated.