I just returned from a Bonnie Hunter workshop. One suggestion that she told us is the same as many who posted, and that is to have the line of the ruler ON the fabric, not off of the edge. This gives you the cut that allows for sewing and pressing because both take up a few threads when sewn and pressed. Also, take your rulers one by one and place them standing up on edge on a flat surface. If you can run a piece of paper under the ruler with no problem, your ruler is warped. Try this with all sides of your rulers to ensure they are not warped or that you haven't 'sliced' off a bit of the ruler over time.