M & W stuff is used in industry, (or used to be ) so should be reasonably accurate and long lived.
VERY few of us can even maintain our shops at a closely controlled 20C, let alone controlled humidity, so we do not work under Standards Room or calibration Room conditions.
If we can REALLY get within a 0.0001", consistently, we have done very well.
If we really want to chase sub micron dimensions, the ratchet on every micrimeter needs to be calibrated so that the force exerted distorts the frame by a controlled amount, in our closely controlled environment.
Somehow, I don't see that happening
Howard