Hi! I've been quilting forever (it seems like) and have purchased many gadgets for the perfect HST. The best thing I have found is pretty new....a bloc loc ruler. They are kinda pricey but the technique ends up with perfection!!!! I don't do alot of large blocks so the 6" square ruler is the one I grab all the time. The ruler has a ridge on the back of it that hugs the seam. Check out their website for a demo. Happy Quilting!!!!