I was wondering if anyone could give me a work instruction for verifing a combination square. We use combo squares to check 90 degree angles and are spending a ton of money to get them calibrated outside. I want to do a verification in-house of all the tools that are verified and not calibrated. By this I mean tools that if found to be out of tolerance are thrown out since they cannot be changed. I can do the steel rule of the combo square but I do not know how to verify the 90 degree angle. We are a very small company but all of our shop guys have these squares. If someone could help that would be great.