Repeatability vs reproducibility
Repeatability holds everything constant except time; reproducibility changes operators, instruments, locations or days. The gap between them reveals hidden influences.
Ten readings taken in a row by one person with one thermometer describe repeatability. The same measurement made on different days, by different people, or with a different thermometer of the same type describes reproducibility. If the reproducibility spread is much larger than the repeatability spread, some influence — the operator, the environment, the instrument — is not under control.
In practice
- Use repeatability for the within-run Type A component of a calibration.
- Use reproducibility (intermediate precision) when the result will be used across days or operators — for example, a laboratory's routine calibration uncertainty.
- A large gap is a diagnostic: investigate before quoting the smaller number.
Frequently asked questions
- Which should appear on a calibration certificate?
- The uncertainty should reflect the conditions under which the certificate's result was obtained; laboratories typically include an intermediate-precision component derived from control charts.
References
- [1]JCGM 200:2012 — International vocabulary of metrology (VIM), 3rd edition
- [2]JCGM 100:2008 — Guide to the expression of uncertainty in measurement (GUM)
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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