MintLP arc protractor

I'm talking to Yip about a protractor for a Rega RB-300 mounted on a VPI HW-19 Mark III. To verify the desired 222mm spindle to pivot distance I cut a piece of cardboard 222mm in length. I measured from the spindle to the center of the armboard mounting hole. It looks to be spot on at 222mm. Is there a more accurate way to measure so that I can confirm my initial findings?

Wendell