Re: Pixel density

[Reza Yahoo]

If we have the physical screen dimensions,  then we can calculate an 
approximate ppi. Its approximate for the reasons you list below. Some phone 
sites even label all their ppi specs as approx since is isn't exact. Doing it 
this way allows us to store a single number (with no unit), allows a simple 
calculation to get the screen dimensions,  and allows users to easily 
understand the quality of the screen (100ppi vs 480ppi).