Having confidence in measurement results requires a quantitative statement of the quality of the results, with such a statement taking the form of measurement uncertainties associated with the results.

However, in itself such information is insufficient. It is necessary to have in place a credible basis for the measurement results and the associated uncertainties. The basis constitutes traceability of the measurement results, through an unbroken chain of comparisons, to stated references, typically in the form of standards held by national measurement institutes (NMIs). In today's global economy, this basis is strengthened by the consideration of the equivalence of measurement across nations by their NMIs participating in interlaboratory comparisons, known as Key Comparisons, through a mutual recognition arrangement (MRA).

We aim to support the Consultative Committees of the CIPM, who have responsibility for organizing Key Comparisons, in terms of the design of such comparisons and the evaluation of the data obtained from them. In particular, we aim to promote a framework for Key Comparisons based on good practice in modelling and uncertainty evaluation.

A discussion of some of the relevant issues is contained in the following paper:

Cox, M. G. and Harris, P. M. "Measurement uncertainty and traceability" Meas. Sci. Technol. 17 (2006) 533-540 http://www.iop.org/EJ/article/0957-0233/17/3/S13/mst6_3_s13.pdf