I understand dividing vacuum by 2 and adding a point to get the magic #, but the p.v.'s are marked as E 3 5 6, and E 8 5 0, and # 8 5 8. Three #'s, not two. It seems the Higher the #, the more pressure it takes to close the p.v. w/ your fingers, the one i have in the primary side now is even...