I have always thought I had a good 1/4 inch sew. I am making an optical illusion quilt by Erin Underwood right now where I need and exact scant 1/4 inch. You sew a bunch of wedges to make a circle. It will matter if it is off even a little bit. My 1/4 in was a little off. I think I have it fixed now. I will book mark this, thanks.