   From: Boris Zbarsky <bzbarsky@MIT.EDU> Date: Thu, 27 Oct 2011
15:01:34 -0400 Message-ID: <4EA9AA8E.1090303@mit.edu> To: www-
style@w3.org On 10/27/11 2:34 PM, François REMY wrote: > OK, I
accept your argument. In fact, you just have transformed the
problem > from "we need to have physical units" to "let's make
the pixel unit virtual > to match a physical range". But then,
how well must a "px" match 1/96 inch > per dot ?  Good question.
> Can it be 1/120ipd? Can it be 1/180ipd?  The spec says:
whole number of device pixels that best approximates the
reference  which means that the answer depends on the size of
the device pixels.  It's also not a hard requirement.  But
clearly, if this requirement is  followed then 1/180ipd can't
happen, because you'd just double your CSS  pixel size and use
1/90ipd.... assuming the viewing distance is arms-length.  > I'm
ready to accept that > the size of a screen can remain unknown
in the detail, but you should > always > have an order of
magnitude available to help you