Copied from the USMA site Metric Typographic Units
Typography is an old art and has developed over the years a bewildering variety of mutually incompatible units. The old Roman foot/inch system did not offer originally a unit fine enough for typography, so for instance the following special purpose ad-hoc units were created in various regions: 1 point (Truchet) = 0.188 mm (obsolete today) 1 point (Didot) = 0.376 mm = 1/72 of a French royal inch (27.07 mm) 1 point (ATA) = 0.3514598 mm = 0.013837 inch 1 point (TeX) = 0.3514598035 mm = 1/72.27 inch 1 point (Postscript) = 0.3527777778 mm = 1/72 inch 1 point (l'Imprimerie nationale, IN) = 0.4 mm 1 pica (ATA) = 4.2175176 mm = 12 points (ATA) 1 pica (TeX) = 4.217517642 mm = 12 points (TeX) 1 pica (Postscript) = 4.233333333 mm = 12 points (Postscript) 1 cicero = 4.531 mm = 12 points (Didot) Resolutions of output devices are still frequently specified in dpi (dots per inch), which is the reciprocal value of the pixel size multiplied with 25.4 mm. With the metric system, we have now a well established, consistent, and globally accepted set of length units, ranging from subatomic to cosmological dimensions. The use of archaic ad-hoc special purpose units has become obsolete and should be strongly discouraged. It it time that the typographic community finally abandons it's current unit mess and also adopts the metric system. Metric typographic units are already used in Japan and to some degree in Germany and other European countries. However, the market dominance of US-originated typographic software without proper support for metric units at all levels currently hinders the further deployment of metric typographic practice. Metric typography as described in the new German draft standard DIN 16507-2 works roughly as follows: *Absolutely everything is measured and specified in millimeters.* No more points, picas, ciceros, inches, etc. and all their awful conversion factors. Dimensions are multiples of 0.25 mm, or where a finer resolution is required multiples of 0.1 or 0.05 mm. There is nothing wrong in principle with continued use of font specific units such as the em, as these are not absolute length measurements. Japanese typesetters use the unit Q (quarter) for font sizes, where 1 Q = 0.25 mm, i.e. the same modulus recommended by DIN 16507-2. This measure coincides nicely with the most common pixel size on computer monitors. For example a typical 43-cm CRT screen has a display area of 320�240 mm, divided into 1280�1024 pixels, which makes each pixel 0.25 mm large. Would this system be more acceptable if the name Q was not used at all, just the resolutions mentioned above? Han
