Shouldn't the "pixels per SQUARE INCH" read instead as LINEAR inches?
Why do people get ppi mixed up like that? After all, even FAX machines are 200 dpi, but if they were 200 pixels total per square inch they would only have 14.14 pixels on each side from top to bottom! Let us just test that here for a moment-
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There you go, 14 pixels, if a person wants to check it out, the "dpi" (or "ppi) concept is not the same as pixels per square inch. One letter of the alphabet alone could use up 14 or more pixels. Square inches are not the same as dpi.