Do not trust the zero until you verify the master. A bore gauge is a comparator. It only tells you the deviation from a known standard. If your master setting is wrong, your parts are scrap. Watch the Titans of CNC team demonstrate the proper chain of traceability. They do not guess. They use Mitutoyo Gage Blocks to set the fixture, verify that fixture with a QuantuMike, and only then zero the bore gauge. This is how you guarantee 2.75000 inch precision before the tool ever touches the part. Tag