I was told that Jenny, when she is being filmed, works faster and perhaps less accurate than in actuality--cause no one wants to watch while someone tediously aligns their ruler, etc.
That 1/4" seam sometimes eludes me too--I don't always do the best test of using a couple of accurately cute squares and once sewn together minus 1/2" (for the two seams) that it measures what it should (i.e. 2.5" sq, sewn together should be exactly 4.5" once sewn). when I do I find that even the wt. of the thread can make a difference on that seam. Also, I'm trying to break the steam habit since as a long arm quilter I know that some spray starch and a lot of steam can shrink down wavey borders--so stands to reason that steam would shrink a block too, right?