Therefore, some rules (if I can use that term) Always calibrate or adjust your seam allowance before beginning the sewing and make a test piece to be sure and then USE THE SAME machine for the entire project and never assume the measurement will continue throughout the projejct. For accurate work it is necessary to check and correct as the project goes along.
Holice, this is great...we should all do this BEFORE even starting to sew as frequently it is not possible to start and finish a project on the same machine. Alot of us have different machines that we use; one at home, the smaller one we bring to class, and in my case, a totally different machine that I have at my daughter's house for using while I'm there for a month once or twice a year. This is a great thing to do before sewing each time, making sure your seam allowance is the same, no matter which machine. I think the easiest way to do this is to sew 2 squares together with a seam that is exactly 1/4" (or scant) and keep it and try it BEFORE sewing on any machine. That way you know at once...just put it under your machine foot, hand lower the needle, and move needle for adjustment...and you can do it the very first time you try! Should work on any machine! I'm off to my daughter's on Wed. for a month and will definately do it, cuz I plan to work on some BOM's I have to catch up on and will still need to work on for a few months when I get back here. I tried that once without checking to see it was exact and suffered the consequences when I tried to get it all put together 2 years later as a UFO...took me alot of work to make it look nice!