Dead pixels were the bane of every screen owner's existence. Now they've vanished without a trace. What changed?

If a computer monitor is dying, it displays signs or symptoms like Dim colors, Screen flickering, Color distortion, Dead pixels, Backlight bleeding, etc.

In other words, how many pixels per inch depends on the size and resolution of the screen you're talking about, so we'll have to do some math to get the number you're after for yours.