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1.4.3 Contrast (Minimum) - Large-scale text

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From: David Ashleydale
Date: May 14, 2012 4:02PM

Hi,

WCAG 1.4.3 Contrast (Minimum) refers to "large-scale" text and defines it
as being at least 18 point or 14 point bold.

For one thing, I find this odd because the recommendation for 1.4.4 Resize
Text is to not use "fixed" font sizes like points. Is 1.4.4 still valid in
today's web environment?

For another, what's the best way to determine what "18 point" is in other
measurement systems? There is a note attached to the definition for
large-scale that says 18 point is "roughly" equivalent to 1.5 em or 150%.
And it says, "When fonts are defined in relative units, the actual point
size is calculated by the user agent for display. The point size should be
obtained from the user agent, or calculated based on font metrics as the
user agent does, when evaluating this success criterion." How does one go
about doing this? Am I safe in telling my developers that "large-scale"
text in this case (non-bold) is at least 150%? What if they want to know in
pixels? I saw a chart that said that 18 point is equivalent to 24 pixels.
Does it depend on the ppi of displays and monitors that we support?

Thanks,
David