A while ago a teacher came to our Quilt group and one thing she said was that if your ruler had thick lines you work will be out and adding all the seams with that fraction of an inch out will be big enough to throw your work out. Also check that your ruler is measuring right and with straight lines, use a metal tape measure as it wont be stretched and see if the measurements are right. She said to get rulers with thin lines and if you are getting different sizes make sure they are all the same maker as that too could be throwing your work out. Hope this helps you.