A quantitative clue that USU need to be considered is manifested when a calculated global chi-square-perdegree-of-freedom parameter (χ 2 /df ) that exceeds 1 significantly is generated in an evaluation without consideration of an USU contribution. This is the case especially if care has been taken by an evaluator to eliminate clearly discrepant experimental data, and to consider all known sources of uncertainty (as well as their correlations) in a realistic manner. Unfortunately, it is common practice for evaluators to simply multiply all the input **data** uncertainties by the factor χ 2 /df when this happens, and thus artificially force χ 2 /df to be exactly 1, e.g., see [3,23,25]. This is not considered to be good evaluation practice because it treats all input **data** points equally, e.g., see [79]. Doing so may lead to biases owing to the excessive influence of those **data** points that contribute to the large chi square per degree of freedom. So, it is a poor substitute for actually uncovering the specific origin of the problem (e.g., discrepant **data** points, overlooked known sources of uncertainty, failure to consider correlations, etc.), or for performing a detailed examination of the individual terms that contribute to the calculated global value of χ 2 /df , and only then introducing a targeted USU contribution when no other options for eliminating the problem are envisioned.