I used to have that problem too....now when I make the 2 cuts for the D9P, I line up one ruler on the seam at the amount that I think is the center of the block. Then I take a second ruler and line it up with the second seam just to make certain that if the cut should be at 1 1/2 from the seam....it's 1 1/2 from the other seam. When I'm sure I have it right, I remove the second ruler and cut.