I recently stumpled upon an android tablet claimed featured with a retina screen with 2048 x 1536 pixels, I have never heard of that android tablet have a retina screen because its price is high. Retina means screen with ppi above 300, which is the most detailed picture naked eye can see. iPhone 4 made with a IPS screen with 960 x 640 pixels, there is a formula to help you work out its ppi This figure out iPhone 4 PPI is 330, a little different from 326 that official give, I am confused. Another, all screens woth ppi above 300 can be called retina? Or Retina means a technique Apple own to optimize on ppi base?