Is there a difference between onscreen picas and analog picas? I have a ruler with 6&12PT on one side and inches on the other. The problem I'm seeing is 6p0 lines up with 1inch - but at the opposite end it look like 12inches does not line up with 72p0 (I would guess the pica side being 2-3 points short...) Is this just my eyes playing tricks or is the ruler just wack? It is a Gaebel ruler. Thanks!