Re: What is the difference between ANSI/NCSL Z540-1 Part I and ANSI/NCSL Z540-1 Part
ANSI/NCSL Z540-1-1994 combines the old ISO Guide 25 and MIL-STD-45662A; where Z540-2-1997 is the U.S. version of the GUM (Guide to the Expression of Uncertainty in Measurement).
So, they actually address different parts of the same whole - calibration.
Hope this helps.
Hershal