Measurement uncertainty fundamentals
From the vocabulary to a finished, correctly rounded budget: everything the GUM asks of a calibration user, without the algebra getting in the way.
10 articles · about 35 min · for Calibration technicians, laboratory staff and engineers who must build or check an uncertainty budget.
- 01MetrologyMeasurement uncertainty explainedWhat an uncertainty statement means, how it is built up, and why a coverage factor matters.4 min
- 02MetrologyTen VIM terms every calibration user should knowMeasurand, indication, error, correction, accuracy, precision, trueness, resolution, drift and traceability, as the international vocabulary defines them.3 min
- 03MetrologyType A vs Type B uncertainty: the difference that mattersType A comes from repeated measurements, Type B from everything else. It changes nothing about how they combine, and everything about degrees of freedom.3 min
- 04MetrologyRectangular, triangular and normal distributions in uncertainty budgetsThe distribution sets the divisor that turns a limit into a standard uncertainty: √3 rectangular, √6 triangular, √2 U-shaped. Say which you chose.5 min
- 05MetrologySensitivity coefficients: how input uncertainties reach the resultA sensitivity coefficient converts an input's uncertainty into its effect on the result. For a direct temperature comparison it is 1; elsewhere, derive it.4 min
- 06UncertaintyBuilding an uncertainty budget step by stepWrite the model, list the inputs, evaluate each as a standard uncertainty, apply sensitivity coefficients, combine in quadrature, expand with k. One table.3 min
- 07UncertaintyResolution as an uncertainty componentA digital display of resolution d contributes a rectangular term of half-width d/2, so u = d/(2√3) ≈ 0.29 d. For a 0.1 °C logger that is 0.029 °C.3 min
- 08MetrologyCoverage factor k explained: why k = 2 means about 95 %The coverage factor multiplies combined standard uncertainty to give expanded uncertainty. k = 2 is about 95 %, but only when the distribution is normal.3 min
- 09UncertaintyEffective degrees of freedom and when k = 2 is not enoughk = 2 assumes you know your uncertainty well. When a Type A term from three readings dominates, Welch-Satterthwaite puts k at 4.53 and more than doubles U.4 min
- 10MetrologyReporting uncertainty: rounding and significant figuresReport the expanded uncertainty to at most two significant figures, round the result to the same decimal place, and state the coverage factor.3 min
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