Reply by ScottM

I have access to CMM and optical comparators so it s pretty easy for me. You can register off a flat edge of a board and scribe a line then flip the square and scribe another line. If the 2 are parallel, then it s square. You can pretty much check any 2 squares against each other too. If they are square to each other, then either they are square or they are both out the same amount in the same direction and the odds of that are pretty minuscule. Of course if they aren’t square, you won t know which is true and which isn’t.

- HokieKen

Thanks, good info. I think I’d heard of the flipping the square and comparing parallel before but always forget about it. It’s the highlighted part that I still end up in an argument with myself on!!