Skip to content
VTValiTracAI

Learning path · 10 articles · about 20 min

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.

For: Calibration technicians, laboratory staff and engineers who must build or check an uncertainty budget.

  1. 01MetrologyMeasurement uncertainty explainedWhat an uncertainty statement means, how it is built up, and why a coverage factor matters.2 min
  2. 02MetrologyTen VIM terms every calibration user should knowMeasurand, indication, error, correction, accuracy, precision, trueness, resolution, drift and traceability — defined as the international vocabulary defines them.2 min
  3. 03MetrologyType A vs Type B uncertainty evaluationType A uses statistics on repeated observations; Type B uses any other information. Both produce standard uncertainties that combine the same way.2 min
  4. 04MetrologyRectangular, triangular and normal distributions in uncertainty budgetsThe assumed distribution sets the divisor that turns a limit into a standard uncertainty: √3 for rectangular, √6 for triangular, k for normal.2 min
  5. 05MetrologySensitivity coefficients: how input uncertainties reach the resultA sensitivity coefficient converts an input's uncertainty into its effect on the output. For a direct temperature comparison it is 1; for derived quantities it comes from the model.2 min
  6. 06UncertaintyBuilding an uncertainty budget step by stepWrite the measurement model, list every input, evaluate each as a standard uncertainty, apply sensitivity coefficients, combine in quadrature, expand with k. Eight steps, one table.2 min
  7. 07UncertaintyResolution as an uncertainty componentA digital display of resolution d contributes a rectangular component of half-width d/2, giving u = d/(2√3) ≈ 0.29 d. For a 0.1 °C logger that is 0.029 °C — often the largest term in its calibration.2 min
  8. 08MetrologyWhat the coverage factor k meansThe coverage factor multiplies the combined standard uncertainty to give an expanded uncertainty with a stated level of confidence. k = 2 is roughly 95 % for a normal distribution.2 min
  9. 09UncertaintyEffective degrees of freedom and when k = 2 is not enoughWhen Type A components rest on few observations, the combined uncertainty has limited degrees of freedom and k must come from the t-distribution. Welch–Satterthwaite gives the number.2 min
  10. 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.2 min

Questions while you read?

Ask ValiTrac AI — answers cite the standards and show any calculation.

Open ValiTrac AI

Other paths