Even with the Wondercut ruler the bias is cut before you sew. For me it's slower than the method jillaine describes, with the same results. I like the method where you put two squares together and sew 1/4" in each side of the diagonal because your bias edge is stable before it's cut. It's better to use a walking foot to be sure the sewing process does not stretch the bias. However, if you use enough starch before you cut by any method, it helps stabilize the fabric.