Whether you use the Bonnie Hunter measure thru the center method or an average of three measurements doesn't matter to me. However, pinning the center of the border to the center of the quilt edge, then pinning again, half way between the center and the corner and again at the corner, then additional pins between all those other ones is the answer for me. I used to just cut a length that was long enough (plus) for the border and sew merrily along, but once they were SO wavy I took it off and measured against the opposite side that had fit properly and found that I was almost 2 inches different. Ever since then I measure.