The CIPM Mutual Recognition Arrangement (CIPM MRA) is the framework through which National Metrology Institutes demonstrate the international equivalence of their measurement standards and the calibration and measurement certificates they issue.
The outcomes of the Arrangement are the internationally recognized (peer-reviewed and approved) Calibration and Measurement Capabilities (CMCs) of the participating institutes. Approved CMCs and supporting technical data are publicly available from the CIPM MRA database (the KCDB).
APMP believes that using the outcomes of routine calibration services provided by NMIs and DIs that have appropriate CMCs registered in the KCDB provides an efficient method of obtaining appropriate evidence to support the submission of CMCs in some cases*. The difference between the measurement result obtained by the NMI submitting a CMC claim and the result of a routine calibration provided by the other NMI can be used as supporting evidence in a similar way to the use of the degree of equivalence (DoE) from a comparison, provided that the process will be transparent and impartial. This process is called a Hybrid Comparison (HC) in that it is neither a Key or Supplementary comparison nor a pure calibration service, but something in between.
The basic flow diagram of a Hybrid Comparison as follows includes sequence of calibration, artefact transfers and report transmissions.
Under current procedures, participation in an international comparison (IC) is, in many cases, the strongly preferred method of providing evidence to support a new or revised CMC submission. This requirement presents difficulties for some APMP members, particularly developing NMIs, because:
The time intervals between ICs in a given field of metrology are very long;
For some simple calibration services, ICs have never been conducted;
Each IC takes a long time;
Developed NMIs must participate as link labs in many ICs on a voluntary basis.
For more information, including principles, procedure and application form of a Hybrid Comparison, please refer to:
APMP Guideline for Using Hybrid Comparisons as CMC evidence