Marti Michell has made all these sizes for NINE PATCH blocks. These make sure that you have created your blocks correctly. 

If the ruler does not align perfectly, either you did not cut accurately, sew accurately or press carefully. 

You can make an adjustment and repeat the test. If your machine needle has multiple positions, try moving it one step at a time until you get a perfect 1⁄4 seam. If the machine came with a screw-in seam guide accessory, try using it, or make a seam guide with a strip of tape 1⁄4 away from the needle hole in the throat plate of the machine.

Marti Michell Nine Patch Ruler-Amber Acrylic Etched - 2 in