To determine the scant 1/4" I sew three strips that are cut an accurate 1.5" each together. Press like normal and then measure the center strip-it should be exactly 1". If it's not adjust your needle position and try again. I hate doing this test-it's really boring-but it's worth it. Sometimes I feel like I moved my needle a bunch but the measurement is the same and sometimes I barely move it and the measurement is way off the other direction. Eventually I get it right. So keep plenty of scraps on hand for testing.