Originally Posted by Holice

All the adjustments might have been made to assure the accuracy of the seam allowance but other factors may play into the finished seam. For example: The way you sit and feed the fabric under the foot may have an effect. I tend to feed the unsewn seam a bit to the left and have to constantly make sure that it is going in straight. I even mark a spot well in front of the foot to make sure I keep the fabric straight.