Starrett or Mitutoyo used on ebay if needed. I have 30 year old starretts that are still perfect at calibration time. I would suggest you not rely on a straight edge to check your plates as you really can not get down into the deeper wear areas from the side seals. Use a dial indicator and stand if you can borrow one. Or take a road trip and we can resurface them in a day to .0001 flatness.