This method may be used when the available experimental **data** can be grouped into two or more distinct sets according to the experimental methods employed in the measurements, as mentioned above in discussing Clue 5. The USU contribution, when evaluating a single physical quantity, can be determined from the standard deviation of the various evaluated mean values obtained by analyzing the several **data** sets separately, according to the distinct measurement techniques (without regard for USU ). However, if there are only two groups of **data** to consider, based on the measurement techniques, the best estimate of the USU contribution probably should be the actual difference in the evaluated mean values for the two groups (see, e.g., Sect. V E 4). If more than one physical quantity is evaluated, similar procedures can be applied separately when considering each of the individual quantities being evaluated.