- From: Gayle Kidder <reddik@sandiego.com>
- Date: Thu, 17 Jul 1997 13:07:42 -0700
- To: davidp@earthlink.net, www-style@w3.org
In a response to another poster (and a slightly different question) David Perrell wrote: "I believe the method most likely to give a reader legible type is to use only em or percentage values because these numbers will be relative to the reader's preferred size. ... For example, you might want to specify font-size for P at 1.2em and font-size for H1 at 2em. Your paragraph text will then be 1.2 times as large as the reader's preferred default for BODY and your H1 headings will be 1.7 times as large as your paragraph text." I've seen this opinion expressed several times on this list. However, my experiments with both NS4 and IE4(p2) show that the example does not work as given, and indeed it shouldn't. An em (which is inadequately defined in CSS1) is, as best I can understand, the total size of the font, measured more or less from the bottom of the descenders to the top of the ascenders, or roughly the width of a capital M in the font. (Historically this gets very complicated, but let's start from there.) If I specify a font size of 1em, then, it comes out considerably larger than the default body type size of the user. I've experimented with several different default fonts and sizes and find that in order to approximate the user's default size you need to specify something between .6 and .8 em, with .8em being the most reliable conversion among those I tested. This, of course, varies with the font... and to a certain extent with the browser. For those of you who are interested, I've posted a demo with an assortment of common Windows fonts at: http://www.beachmedia.com/www/emsizes.html Therefore, I can't see how one can advocate starting with an em as the recommended unit for an initial font spec, since users' default fonts are liable to vary considerably. Or can one recommend a standard conversion value for an em to user's default, say .8? Another typographer friend of mine has this to say: "[Designating font sizes in ems] is literally nonsensical in traditional terms. An em is a unit of space; 12pt is a unit of size ... it is meaningful to say "a 12-pt em" or "a 12-pt font" but not a "1-em font" -- the size of the em varies according the size of the font, not vice versa." Yet I seem to see designating font sizes in ems being advocated in this group. Do I misunderstand? Any clarification gladly solicited. Gayle Kidder
Received on Thursday, 17 July 1997 16:10:47 UTC