The distinction between error and uncertainty is that error
Answer: D
The error of a particular measurement is a definite but unknowable number, and the uncertainty is the interval within which it is believed to lie. Modern practice reports the second because the first cannot be known, and confusing them leads to statements that cannot be checked.
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An instrument's specification of accuracy applies
Answer: A
Temperature range, humidity, warm-up time, orientation and supply stability are all part of the specification, and using the instrument outside them invalidates the figure. Reading the small print before the measurement is what distinguishes a result from a number.
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Repeatability and reproducibility of a measurement differ in that reproducibility covers
Answer: B
Repeating a measurement immediately with the same setup gives the narrower figure, and repeating it in another laboratory with other apparatus gives the wider one. Which is quoted matters greatly when a result is being compared with someone else's.
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A round-robin or intercomparison exercise between laboratories establishes
Answer: C
Circulating one artefact and comparing the reported values against the claimed uncertainties reveals any laboratory whose confidence exceeds its performance. It is how accreditation bodies keep the whole traceability chain honest.
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The uncertainty budget of a measurement is
Answer: D
Listing each source, its magnitude, its distribution and its sensitivity coefficient makes the combination auditable and shows at once where an improvement would pay. It is the working document behind any quoted uncertainty.
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A sensitivity coefficient in an uncertainty budget expresses
Answer: A
Multiplying each input's uncertainty by its coefficient converts them all into the units of the result so that they can be combined. An input the result barely depends on can be measured crudely, which is often where the effort is best saved.
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A Type A evaluation of uncertainty is one made
Answer: B
Repeating the measurement and computing the standard deviation of the mean is the Type A route, and everything else, from certificates to handbook data to reasoned judgement, is Type B. The distinction concerns how the figure was obtained rather than its quality.
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Coverage factor in a statement of expanded uncertainty is applied to
Answer: C
Multiplying the combined standard uncertainty by two gives roughly ninety-five per cent confidence for a normal distribution, and the factor used has to be stated with the result. Omitting it makes two quoted uncertainties incomparable.
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A result quoted as 100.0 plus or minus 0.2 with a coverage factor of two means that
Answer: D
Dividing the expanded figure by the coverage factor recovers the standard uncertainty, and the factor of two corresponds to about ninety-five per cent for a normal distribution. Reading the interval as a guarantee rather than a confidence statement is the usual misunderstanding.
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Significant figures in a reported result should be chosen so that
Answer: A
One or two figures in the uncertainty and a result rounded to the same decimal place is the convention, which conveys the resolution honestly. Quoting six figures against a one per cent uncertainty misrepresents the measurement as badly as rounding away real information.
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