The drawing that is posted below is at a 1/2 scale so the 20" dimension is at 10 inches so your measurements will be off by 1/2. Some of you are already have discovered this problem.
So here is the Illustrator file : 1412_Sp08_XXX_Sandbox_100ptWork_1to1scale.ai
and here is the dwg file : 1412_Sp08_XXX_Sandbox_100ptWork_1to1scale.dwg
XXX is representative of your initials...MLG, BTR, ect. ect.
Have fun....