I use the Simple Folded Corner Ruler
https://www.google.com/search?safe=a...31.IzCQGgLzCZs for those tricky hst and flying geese units. I felt so guilty buying it at first, for a Bonnie Hunter mystery quilt, because it was the most expensive ruler I had ever bought! But now I use it all the time! It's large enough to use for squaring up units too.