My very first quilting supplies purchase was a package that came with a small cutting mat, rotary cutter and 6 x 18 inch ruler. Along with a quilting 101 type book. Nothing ever came out accurate, everything was too short, but I kept fussing along. One day I used my husbands carpenter's ruler, the metal roll up kind, and measured that ruler. Come to find out, the 1/4 inch mark was not a full 1/4 inch. It's a wonder I hadn't given up on quilting before I found that out. Needless to say, I bought a better ruler!