I use a 12 1/2 ruler too. Actually this is such a common size block I use it a lot. I am teaching the Underground Railroad to newbies right now and that is our final step with each block. They are developing a better understanding of the need for good 1/4 in seams and we are only on block 3. I try not to be really hard on myselF and am not hard on others but a bit of work teaches you the benefits of accuracy. I just am not going to ever be quilt police crazy. They take all the fun of it. But accuracy is important so I guess my goal is to be balanced. I have taken blocks apart and resewn them and although it is no fun it is sometimes necessary. And always it helps me learn!!!