PPI Question

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http://forums.androidcentral.com – So i know the HTC One has a PPI of 468 Pixels per inch! But my question is that pixels per inch squared or is it just a linear pixels per inch? And is 468 really that big of a step up from 441? I am already set on the phone but i feel like reviewers are boasting the Pixel density but i feel like from 441 to 468 isnt a big change (HowTos)