Stitch n' Snip Mini HST Square up Ruler help you square up 2 1/2", 2, 1 1/2" raw edge to raw edge HST fast and easy.
Directions to use ruler:
Sew a traditional HST by cutting 1/2" larger than the size you want the HST trimmed to (example, cut a 3" square to trim to a 2 1/2" HST).
Mark a line from one corner to the opposite corner of the square pairing. sew 1/4" from the center on each side of the line. Cut on the line to get 2 HST per pair of squares.
Using the ruler line up the corresponding line on the seam that you sewed. Trim both sides and then trim the "dog ears" off. Press to the dark fabric carefully.