Most readable line lengths?

["Geoff Hart (by way of \"Eric J. Ray\" <ejray -at- raycomm -dot- com>)" <ght -at- MTL -dot- FERIC -dot- CA>]

Sarah Wigser has been <<tasked with researching "the most readable
line lengths for 11 point type". This is kind of out of the ball park
for me - any pointers?>>

First pointer: Ignore any recommendations that involve inches or
centimetres. Fonts vary enormously in their actual physical size for
a given point size (e.g., Times 10 is much larger than Garamond 10),
so measured line lengths are a bad metric.

Second pointer: The rule of thumb for line lengths is usually that
a line should be between two and three "alphabets" long; 2.5 times
works well for me in most cases. That is, type a...z twice,
measure the length, then add 50%. This works surprisingly well as a
starting point, which leads to pointer number 3:

Third pointer: Why does this rule of thumb work? Well, line lengths
should be such that they minimize back and forth (left to right) eye
movement, without eliminating these movements completely. If you
glance at a line of type and pay attention to what your eyes are
doing, you'll see that your field of view takes in (clearly) a
certain amount of space, with a fair bit of text lying there, fuzzy,
just outside this visual field. Count the number of characters, and
multiply it by 2 to get the line length. For example, I just tried
this with the 11-point Garamond in our annual work program and
counted a total 34 letters. If I permit myself one shift of my visual
fields to the right on each line of type (i.e., if I add another 34
letters), I end up with a total of 68 letters, which (surprise!) adds
up to almost exactly 2.5 alphabets (2.5 X 26 = 65). My colleague
Simon, a graphic artist with much better vision, did the same test
and came in at 82 characters, which is pretty close to 3 alphabets (3
X 26 = 78). No, I didn't fudge my numbers... that's exactly what we
counted. Maybe those thumb rulers knew whereat they spoke!

Don't forget that line length is only part of the equation. To make
text legible, you have to use an appropriate amount of leading (line
spacing). Unfortunately, I can't offer an equally good rule of thumb
for leading, other than that setting lines solid is too tight and
setting them "doublespaced" is usually far too wide. The goal is to
produce a line spacing that lets you scan to the right end of a line,
then return your eyes to the start (left edge) of the next line
without skipping lines. That's the minimum line spacing; you can add
more for aesthetic effect.

This concludes our "do-it-yourself" cognitive psychology lecture for
the day. We now return to our regularly scheduled broadcast...
--Geoff Hart @8^{)}
geoff-h -at- mtl -dot- feric -dot- ca

"Patience comes to those who wait."--Anon.


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