We've had a few customers ask for this nifty tool and you can now find it at Piece by Piece Fabrics. The brilliant design will help you square up your blocks quickly and accurately. There is no rocking as your ruler pivots over the top of the seam allowance.
The ruler comes in many sizes. We are carrying the 6 1/2" square and a versatile set of three that will cover most of the sizes that you will ever need to make. Check out the manufacturer's website blocloc.com and come in and get yours at the store!