This technical report provides guidance in assessing the reliability of a statement of measurement uncertainty in question, that is, in judging whether that stated uncertainty can be trusted to include the values that could reasonably be attributed to the measured quantity (measurand) with which that stated uncertainty is associated. This report is most applicable to statements of uncertainty in the results of dimensional measurements based upon the ISO Guide to Expression of Uncertainty in Measurement (GUM). (Also called ANSI/NCSL Z540-2.) This technical report helps parties to avoid potential, or resolve actual, disagreements over the magnitude of a stated measurement uncertainty, particularly when that uncertainty is part of a determination of conformity of a manufactured product to a dimensional specification.