Ken,
You are fortunate. Most of the ASTM's now have a Precision and Bias section, which is the MU for that method. A few of the standards actually have a section that makes sense. ASTM, like most test labs, is struggling with the MU issue.
A primer on MU specifically for test labs has been written and is in review.....once I know it is about to publish, I will post info in the book section. It is in very simple language. More than that I am not allowed to reveal just now.
Hershal