The triad of trust: solutions to practical inconsistencies in T, T90 and in situ traceability

The 2019 redefinition of the kelvin and its accompanying Mise en pratique (MeP-K) herald a bold new future for the thermometry community. The MeP-K offers a blueprint for putting the kelvin into practice, and the proliferation of the new realization options it enables will lead to both benefits and practical inconsistencies for thermometer users. Users have been accustomed to a straightforward International Temperature Scale of 1990 T90 measurement chain with traceability and trust assured by national metrology institutes (NMIs). In contrast, the emerging world of coexisting T and T90 thermometers, with some offering in situ temperature traceability unconnected to NMIs, will challenge this straightforward measurement chain. Here, we discuss practical solutions to the practical inconsistencies users will encounter. These solutions focus on the triad of trust in metrology-traceability, equivalence and competence-to allow thermometry end users to broadly benefit from new technologies while maintaining trust in measurements and minimizing net disruption. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.