After reading some of the doomsday reviews, I was a little afraid to buy this. But, it was the least expensive and I just couldn't fathom how such a simple tool would be so hard to get right. When I received it, I compared it to an aluminum one that cost 2.5 times as much. They were identical in size and when placed end to end on all 4 sides, they both appeared perfectly straight to the eye. No sharp edges beyond what I would have expected.I'm sure Mr. Retired Engineer Man could inspect it with his electron microscope and other highly scientific tools and find some variations and deviations, but for determining if a few frets are not level on a guitar, it works perfectly for me.