I have found that when I square up each component of a block that I usually end up with the right measurement block. I'm not saying that I don't make mistakes that way, because I do. Usually if the mistake doesn't jump out at me, I will leave it be. However, when I lay out the finished top, if there is a block going the wrong way, I will rip it out and place it the right way. usually my DH is the one to point out my mistakes, so I don't have to go looking for them; which makes me happy (don't think so), but he usually points out glaring mistakes and the not so little I can let it go ones. The Amish supposedly put in a mistake into every quilt because only God is perfect. Well, I don't have to deliberately do that now.