W3C home > Mailing lists > Public > w3c-wai-ig@w3.org > January to March 2000

pixels, points, ems, ???

From: Charles McCathieNevile <charles@w3.org>
Date: Thu, 20 Jan 2000 18:05:42 -0500 (EST)
To: John Nissen <jn@tommy.demon.co.uk>
cc: WAI IG <w3c-wai-ig@w3.org>, don@jnd.org, wai@tommy.demon.co.uk
Message-ID: <Pine.LNX.4.20.0001201801410.1521-100000@tux.w3.org>
In Don's question reproduced below he has correctly identified the problems
with using pixels (px) or points (pt) as sizes for stylesheets.

My recommendation is to set the basic size in centimetres or inches and have
it inherited. Then set everything else re;lative to that, ie in %, em or ex.

Not only is 2.54 cm and 1" the same thing throughout the real world (and
perhaps even throughout the browser world, although I wouldn't be overly
trusting of it) but using that approach allows people who have some reason
for wanting very large or very small fonts to easily set it up with their
style sheet (using a proper CSS-capable browser, of couse...)

Charles McCN

On Thu, 20 Jan 2000, John Nissen wrote:

  Hello, web access folks,
  Human factors guru, Don Norman (author: the Psychology of Everyday Things)
  has raised an issue on the CHI-Web list.  Perhaps somebody from WAI
  could answer this one.
  A good thing is that he mentions "users who are older or visually
  impaired".  These users were not part of his thinking until recently,
  when he admitted he should take them into account.  However I question
  his reason for wanting to control absolute size precisely.  And I don't
  think he has quite got the concept of relative size - presumably
  he wants to have a variety of text sizes.  
  Could somebody reply?
  Cheers from Chiswick,
  Forwarded message follows:
  >Date:         Wed, 19 Jan 2000 14:06:49 -0600
  >Reply-To: don@jnd.org
  >Sender: "ACM SIGCHI WWW Human Factors (Open Discussion)" <CHI-WEB@ACM.ORG>
  >From: Don Norman <don@jnd.org>
  >Subject:      points versus pixels (or ems)
  >We are having a (happy) fight, whether to specify text size in points or
  >pixels or ems in our style sheets.
  >The goal is an appropriate combination of control over aesthetics and to
  >ensure readability of text, even for users who are older or visually
  >impaired, yet without such huge text size that information density is
  >So there are two questions: Whether to specify fonts in our style sheets by
  >pixels or points (some say ems), and then, what choices to make.
  >The argument for points is that it is an international standard, with one
  >point equal to a precise physical measurement. So in theory having specified
  >text in points, it will always be the same physical size, regardless of
  >brand of computer, monitor, OS, browser,, screen resolution setting, or even
  >if printed on paper.
  >The argument against points is that the theory is false in practice. Mac
  >points are different than PC ones, Microsoft is different than Netscape
  >(even on the same screen at the same time) etc. and etc.
  >The argument for pixels is that this is becoming the standard way of
  >controlling sizes, that it works (sort-of) across browser brands, OS, etc.
  >And that because most web pages specify tables and object placements in
  >pixels, specifying text in pixels yields more consistency.
  >The argument against pixels is that this is very very hardware dependent.
  >Different brads of monitors, CRTs versus LCDs, and different display
  >resolution settings yield different physical sizes of pixels.
  >So fellow CHIers -- what is your experience. Wouldn't it be nice if someone
  >had actually done a careful informed empirical study.
  >Don Norman
  >Donald A. Norman
  >  President, UNext Learning Systems, UNext.com
  >  norman@unext.com
  >Personal: don@jnd.org  http://www.jnd.org
  >Nielsen Norman Group
  >norman@nngroup.com    http://www.NNGroup.com
  >User Advocacy is the passion, Human-Centered Design the means.
  Access the word, access the world       Tel/fax +44 20 8742 3170/8715
  John Nissen                             Email to jn@tommy.demon.co.uk
  Cloudworld Ltd., Chiswick, London, UK   http://www.tommy.demon.co.uk

Charles McCathieNevile    mailto:charles@w3.org    phone: +61 (0) 409 134 136
W3C Web Accessibility Initiative                      http://www.w3.org/WAI
21 Mitchell Street, Footscray, VIC 3011,  Australia 
Received on Thursday, 20 January 2000 18:05:47 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 13 October 2015 16:21:07 UTC