A pixel is not a pixel
http://www.quirksmode.org/blog/archives/2010/04/a_pixel_is_not.html [www.quirksmode.org]
2016-11-20 19:17
CSS pixels vs device pixels. More information in presentation slides.
http://www.quirksmode.org/presentations/Spring2012/mobeers.pdf
https://fronteers.nl/congres/2012/sessions/a-pixel-is-not-a-pixel-peter-paul-koch