I used to use a ruler that had really wide lines. I found that depending on whether I was tired, or didn't cut it all in one go, I would go to the left side of the line one time & the right side another. Then I would have different sizes & nothing went together as planned. Altho I just picked up Mary Ellen's books as my sister went to a lot of her classes & used her PPM method & won 2 award for her quilts. They looked beautiful!!!!