Trick ruler - photo

[BuffaloJohn]

I just had something like this I dealt with. I had an L square with silk screened scales. It turned out that the ruler was printed with 25mm to the inch instead of 25.4mm to the inch.

I was trying to measure something and had used a different scale to estimate and was using the L square to try to get it more accurate. For the life of me, it was always off, so I thought, well maybe the square is not square, so I held it up against a framing square and it was square, but the numbers and lines didn't line up. There is was, each inch was off a little and it increased by length. So I checked the mm side and it was off as well.

I immediately pulled out the acetone and obliterated all of the markings. As a square it was fine, but ALL the markings were wrong.