Reporting uncertainty for gas certified reference materials: balancing customer requirements with calibration and measurement capabilities


The effect of rounding when presenting the uncertainties associated with bespoke gas certified reference materials has been investigated. This has been examined in the context of wanting to provide the customer with as close a match as possible to what was originally contracted whilst needing to comply with the minimum uncertainties allowed by internationally agreed calibration and measurement capabilities under the International Committee for Weights and Measures’ Mutual Recognition Arrangement or other scopes of accreditation. The effect of rounding has, in relative terms, been shown to be large in some cases and this has prompted an investigation into improved methods to express more precisely values presented on certificates accompanying bespoke gas certified reference materials. This has included a new proposal to present relative, instead of absolute, uncertainties on certificates thereby matching exactly customer requirements. This Practitioner’s Report also demonstrates how considerations of customer and quality system requirements should be properly balanced and how internal review of technical procedures leads to continuous improvement.

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    Because the analysis of gas mixtures is relatively simple compared to liquid and solid mixtures in terms of sampling, homogeneity, extraction, analytical interferences, etc., the concept of a gas CRM is very closely related to a gas calibration standard, with certified stability often being the only difference.

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    If material is lost or decays during preparation, its certified value may then relate to the value determined by analysis instead, but the following discussion is valid nonetheless.

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The funding of the National Measurement System by the Department for Business, Energy & Industrial Strategy is gratefully acknowledged.

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Correspondence to Richard J. C. Brown.

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Brown, R.J.C., Brewer, P.J. Reporting uncertainty for gas certified reference materials: balancing customer requirements with calibration and measurement capabilities. Accred Qual Assur 26, 41–45 (2021).

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  • Uncertainty
  • Significant figures
  • Reference materials
  • Accreditation
  • Rounding