This Standard provides guidelines for evaluating the uncertainty of test values obtained when verifying dimensional measuring instruments1 to an ASME B89 testing protocol. The scope is limited to the case in which the test measurand is the error of indication at a rated operating condition, hence, test measurands such as the “worst possible” error of indication that might occur at any operating condition (including those conditions that are not tested) are outside the scope of this Standard. ASME B89 testing protocols are composed of many individual tests, each test yielding one test value that is an estimate of the instrument’s measurement error at the particular operating condition tested, and this test value is compared against the maximum permissible error (MPE) (specified for that rated operating condition) using the protocol’s decision rule. Although the MPE is specified by the instrument manufacturer for all rated operating conditions, the test value uncertainty is associated only with the test value obtained at the particular operating condition prevailing at the moment the test value was obtained (unless a correction to the indication is performed that is allowed by the test protocol). Because each test investigates the error of indication at a particular rated operating condition, the test value uncertainty does not include the robustness or comprehensiveness of the testing protocol, i.e., it does not address the number of tests or their distribution over different rated operating conditions. This issue is addressed by the standardization committee creating the testing protocol, the committee balances the number of tests against the amount of time and effort to complete the testing protocol. The scope of this Standard excludes issues associated with the evaluation of the uncertainty of future measurement results on workpieces and focuses solely on the test value uncertainties used to verify the instrument’s performance specification. Typically, the test value uncertainty is much smaller than the associated MPE value of the verification test.