This dual purpose ruler allows you to mark the center of your block/strip/fabrics within a 12" span as well as easily mark your sewing lines for half square triangles. There are markings down the center of the ruler, allowing you to align it to any straight fabric edge and mark a quarter inch seam.
It's long enough to fit on a 10" by 10" square, making it perfect for use with Layer Cake squares.
Centering: All you have to do is place the left and right markings at the same number, and the 0 will show you exactly where the center is. If you have an 8 inch block of fabric, place the left-hand 4 on the left side of your fabric, the right-hand 4 on the right side of your fabric, and the 0 will be the exact center.
Half Square Triangles: Place the pointed end of the ruler in the top left corner of your fabric square. Next, using your favorite fabric marker/pencil, draw the diagonal line on both the left and right sides of the ruler. Now you can sew exactly on the lines. After sewing, cut from corner to corner and you'll be left with two half square triangle squares.