[waltjp]

I don't even do the math. I pick up the ball and pace the distance to the next yard line. In this case I'll have 2 yards to A's 45, the 50 makes 7 yards, the B's 45 makes 12 yards, then pace off the 3 additional yards needed. Do not pace off all 15 yards. If the field is marked off well enough that I can determine that the ball was 3 inches short of A's 43 to start I'll mark the ball that same 3 inches from B's 42. In the grand scheme of things that 3 inches isn't very significant.