The Fluke reference is good, except it has one flaw.....the writer refers to a TUR for the 10:1 and 4:1 rules.
Under ANSI/NCSL Z540-1-1994 and the previous MIL-STD-45662A, that was acctually a TAR, becuase measurement uncertainty (MU) was virtually unknown for practical application outside of a NMI at the time the standards were written.
What does that mean? Use the TAR to find out how accurate your standard is compared to the unit being calibrated. Then the MU must still be calculated, regardless of the accuracy ratio.
Guardbanding cannot be successful without knowing the MU, and remember that while the accuracy ration feeds into MU, it is only one influence.
Hershal