I use the center measurement for my borders and they turn out nice and flat and even. I cut my border strips extra long. Then I fold my quilt in half lengthwise and I lay a strip of the border along the fold and mark both ends and cut two border pieces. I sew the border strips on the long edges of my quilt, press and trim and then fold the quilt in half the other way. I lay two more border strips along the new fold and mark both ends and cut and sew. I match the center point of my quilt edges with the center point of each border strip to make sure I get the border on evenly. This technique is so simple and I don't have to measure the length of the border strips. It also allows me to use my bed and I don't have to crawl around on my hands and knees on the floor.