What is measurement uncertainty and how should it be reported under CBM T6?

• A. A single value representing instrument accuracy.
• B. The range within which the true value lies; report with method, components, and coverage factor (k).
• C. A range that excludes any method details.
• D. Only include the coverage factor, without method or components.

Answer: (B)

Measurement uncertainty is the quantified doubt about a measurement result. It defines a range around the reported value within which the true value is believed to lie with a stated level of confidence. Under CBM T6, reporting uncertainty goes beyond a single instrument accuracy number; it reflects how all sources of error contribute to the measurement. The report should show how the uncertainty was determined, list the components that contribute to it (such as type A statistical and type B systematic uncertainties), and include the coverage factor used to obtain the expanded uncertainty. In practice you present the measured value with the expanded uncertainty and the associated confidence level, for example a measurement of length might be 25.00 mm ± 0.10 mm with k = 2, indicating about 95% confidence. This approach communicates both the size of the doubt and how it was derived. A single value of instrument accuracy would miss other error sources, and omitting method details or only giving the coverage factor would leave the uncertainty incomplete.