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.