I chain piece oversized squares together 1/4" on either side of the diagonal line, cut apart, iron to the dark and use the Bloc Loc ruler to square up. You can see a video on
http://www.blocloc.com/ I just finished making 800-2 1/2" squares for a churn dash quilt and each one came out perfectly. Sure made my life sooooooo much easier. No affiliation, my LQS demonstrated them on Play Day and I was immediately sold.