Eliminate the math from quilting with Finished Size Quilting! Use Triangle Seam Allowance Additions on your quilting ruler and forget that crazy (and inaccurate) fraction you need to add to cut half- and quarter-sqaure triangles. Just snap on the red or green seam allowance addition and cut the finished size you want. The Additions figure out the extra seam allowance you need.
Quilt Market 2010 – Finished Size Quilting