A comment here from a (retired) maintenance man might help a noob getting started. The maintenance man is looking to get it (the target machine) back to running. Absolute accuracy is secondary. I usually didn't have the drawings anyway. When I make a (singular) part, it is to fit the machine as worn in. It might be three months wear, it could be thirty years wear.
To Fit is the primary target.here. As such, the
accuracy(absolute) of a measuring instrument is not so important. The
precision(repeatability), on the other hand, is. Highly so.
A caveat here; Most of my professional background was in electrical and electronics. Two decidedly different crafts there. But precision is precision, whatever the craft. BTW, my calibrations were long before computers. And my calibration standards were a factor of ten, usually NBS tracable. The Cal Lab I used was
one generation removed from the NBS. When I had to make a mechanical part, it usually had the same accuracy as the electrical parts had. A much too tight tolerance. But that's how I was used to thinking.
I realize that professionally I don't fit in well here. But in my day,
basic knowledge of machinist's skill was a part of my profession. Building from scratch a D'Arsenval meter movement was as precise as that of a machinist.
Bill Hudson