Attached Link: http://www.scantips.com/no72dpi.html#3

For what it's worth, the "72ppi for screen" has never had any relation to the physical resolution of the monitor. See the attached link. In general, I never worry about ppi or dpi. I just use the absolute number of pixels where possible, that's the easiest method. I could go at lengths at explaining the differences between ppi, dpi and lpi (I had to do all kinnds of conversions there when I was studying) and the whole Nyquist/Shannon sampling theorem, but that would probably be information overkill. This site would be good introduction (it's intended for scanning, but mostly applies to rendering oto): http://www.scantips.com/basics03.html