Metric Typography Units

From: Markus Kuhn (Markus.Kuhn@cl.cam.ac.uk)
Date: Wed Jan 13 1999 - 20:29:47 EST


Mirko Raner wrote on 1999-01-13 19:00 UTC:
> I would like to know whether there are any standards or maybe ISO
> recommendations about typographic units (eg, point, pica, ...).
> The special problem is that there are two different definitions of the
> unit "point". The PostScript standard treats 1 point as 1/72th of an inch.
> In conjunction with digital typesetting systems such as TeX 1 point is
> defined to be 1/72.27th of an inch.

Asking for an ISO definition of the "point" is the wrong question.
Typography really should only use metric units like *any* other modern
field of science and technology. There is absolutely no need for special
length units in typography.

The relevant standard you are looking for is DIN 16507-2. I don't know
whether there is an ISO or CEN equivalent of it yet, but I think there
really should be one made.

Summary: Like all other non-metric units, points (all of them), picas,
ciceros, cpi, dpi, lpi, etc. are a real mess and should be replaced by
the millimeter as the one and only unit for every length measure in
typography as soon as possible (paper sizes, column width/length/
distances, font sizes, font heights, etc.). Everything else is just
ridiculous historic ballast and it boggles the mind that we still use it
and waste a lot of time with converting units. Surely some old
typographers will turn out to be conservative and mentally inflexible
and express their irrational love for the points, but we can't continue
this unit nonsense forever, even if it means breaking quite some
inertia.

Metric typography as described in DIN 16507-2 works roughly as follows:

Absolutely everything is measured in millimeters. Font sizes are
multiples of 0.25 mm, or if necessary multiples of 0.05 mm. No more
points, picas, ciceros, inches, etc. and all their awful conversion
factors. There is nothing wrong with font specific units such as the em,
as these are not absolute length measurements.

There are two font measures:

  font height: this is usually the height in mm of letters like
                  k or H
  font size: this is the baseline distance for which the font was
                  designed, and this is the measurement by which a font
                  is normally refered to

Normally, the font height is 72% of the font size. If you write say
"Helvetica 3.00" then this means you have a font designed for a 3 mm
line spacing. Calculations become trivial: in a 60 mm high column you
can write exactly 60 mm / 3 mm = 20 lines. No more factors 72 and 2.54,
absolutely beautiful and sensible. If you write "Helvetica 3.00/3.25"
then this means that you use exactly the same font, but with 0.25
mm more baseline skip than it was designed for.

DIN 16507-2 also contains a list of preferred font sizes in mm. This is
a geometric series, similar to the well-known ISO 3 preferred numbers
and the IEC preferred dimensions of electronics components.

The legacy we have to fight with is that typewriters were invented in
the US and most typographic software used today is exported from the US,
and therefore the rest of the world has to suffer under the silly
inch-based Flintstone units and will continue to do so in the 21st
century. It's a real hassle.

Dear typography software and equipment vendors (Adobe, Microsoft, HP,
etc.): PLEASE, PLEASE give us metric font sizes in the style of what DIN
16507-2 suggests and specify raster resolutions in micrometers (and
*not* the reciprocal dots per millimeter, which would just again leads
to conversion factors!).

Dear ISO community: Please start a project to write a standard guide for
the use of a simple and consistent set of metric typographic units. Such
a guide with examples of how to use them would be a really useful
contribution. DIN 16507-2 is available as a good starting point.

Examples for metric dimensions: a typical book font size is 4.25 mm and
a modern laser printer as a resolution of 40 Ám. It really does not take
much time to get used to metric typography.

Markus

-- 
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org,  WWW: <http://www.cl.cam.ac.uk/~mgk25/>



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