Prism is right. I used to strive for the perfect 1/4 inch seam, would measure the seam allowance , got specialty feet, etc. Nothing ever fit quite right and I was very frustrated. I watched a Quilty video about a year ago where Marianne Fons demonstrated something and it was a light bulb moment! Take 2 2.5 inch squares and sew them together, then press them as you normally would. Measure the *unit*, not the seam! If it measures 4.5, you are good, if not, adjust your needle a click or 2 until it measures 4.5 inches. The seam measurement is far less important than the resulting block measurement because everything needs to fit together. I now use my regular foot and know where to set my needle for proper sized units. My accuracy went up dramatically and frustration level is near zero.