 Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results by Barry N. Taylor and Chris E. Kuyatt

Institutional guidance on measurement uncertainty. Sections 2–5 distinguish uncertainty evaluation from the physical classification of effects and combine uncertainty contributions; Appendix D.1 discusses systematic error and correction.

Additional locators: §5.1 and Appendix A, equation A-3: combined standard uncertainty from sensitivity coefficients, input variances and covariance terms.

Sections 6.2–6.3 distinguish an expanded-uncertainty interval from an automatically justified confidence level. A coverage factor of two gives approximately 95 percent under a normal model when the combined standard uncertainty has negligible uncertainty; a precise confidence interpretation otherwise requires distributional information. ^[ref]

Appendix A.1 states that the measurement model should include corrections and all quantities contributing significant uncertainty, rather than express only a physical law. ^[ref]