I discovered that one of my Olfa frosted rulers was off. It wasn't misprinted, it was miss-cut. It was too large by about 2 threads width on 2 sides of the ruler. I had actually been drawing with it and couldn't figure out why my drawing was off kilter, then I measured the ruler. I had recently purchased it; when I returned to the store and showed the clerk, we both inspected their whole stock of that ruler. Every single one was off.