Who invented this thing? Looks like one company did and everyone else copied it.
You are suppose to check many of these countersink gages on a surface plate and makes sure it reads to what is set on the back of the gage. I notice that in the Mitutoyo catalog that their countersink gage comes with a setting master (a ring gage). What is the reason that many of the other countersink gages don't come with a setting master (a ring gage) ? You are just suppose to check it on a surface plate to the number imprinted on the back of the gage and set it to that and not question this method? What happens if the countersink gage wears?