"Best Measurement Capability" is Ousted;
"Calibration & Measurement Capability" is Favored

By international agreement, the phrase traditionally used by calibration labs to describe the accuracy which they can achieve in their measurements is to be replaced during 2010.

Announcement made by the International Laboratory Accreditation Cooperation

Best Measurement Capability (BMC)
Change in Terminology to
Calibration and Measurement Capability (CMC)

Metrological traceability is disseminated to the market by Accredited Laboratories under the ILAC MRA and by National Metrology Institutes under the CIPM MRA. This provides reliability without frontiers for measurements across the world.

The capabilities provided by accredited calibration laboratories have in the past been
described by the Best Measurement Capability (BMC) which expresses the lowest uncertainty of measurement that could be achieved during a calibration. This terminology has been widespread in accreditation around the world.

The National Metrology Institutes (NMIs) have had a similar description of the services provided to their clients. Within the NMI community the term has been Calibration and Measurement Capability (CMC). The BIPM and the Regional Metrology Organisations (RMOs) have in cooperation with ILAC and the Regional Accreditation Bodies (RABs) investigated the difference in terminology and have arrived at the following conclusion:

"In the context of the CIPM MRA and the ILAC Arrangement, and in relation to the CIPM-ILAC Common Statement, the following shared definition is agreed :
a CMC is a calibration and measurement capability available to customers under normal conditions:
(a) as published in the BIPM key comparison database (KCDB) of the CIPM MRA; or
(b) as described in the laboratory’s scope of accreditation granted by a signatory to the ILAC Arrangement. "

In pursuit of harmony and co-operation between the communities; ILAC has decided to make a change in the terminology used and in the future the BMC will be named as the CMC. The intention is to achieve harmonisation of terminology in the dissemination of metrological traceability worldwide regardless of source.

• BIPM-ILAC paper explains the reason for the decision
• ILAC circular

FAQ Prepared for Accredited Labs by UKAS

It is likely that accrediting bodies in other countries would offer similar advice.

Q :  What is this change?
A:  We are changing the term used to describe a laboratory’s measurement capability from BMC (Best Measurement Capability) to CMC (Calibration and Measurement Capability).

Q: Why is this change being made?
A:  This change was agreed by ILAC (The International Laboratory Accreditation Cooperation) with BIPM (Bureau International Poids et Measures)  in order to harmonise the practices of the NMI (National Measurement Institute) community and the accreditation community.

Q: Do I have to recalculate my uncertainties?
A: No, the calculations are unchanged.  Only the words describing the capability are changing.

Q: What is UKAS going to do about this?
A:  We will change the term used on your Accreditation Schedule over the next few months to use the term CMC instead of BMC.  The change will be undertaken by the end of 2010.

Q: What do I have to do?
A:  You should change the term used in any advertising or other literature from BMC to CMC.  It is expected that your next review or reprint would address the change. You should not change your calculations as a result of this change.

Q: Is the assessment or surveillance programme for my laboratory affected?
A:  No, this will continue unaffected, except that assessors will expect to see the term CMC increasingly in use, rather than BMC.

Q: Are BMC and CMC really the same?  How can I be sure?
A: The definitions used by the two communities were already aligned.   CMC describes the realisable measurement capability of a laboratory and includes the attributes of a relatively ideal artefact being calibrated.

Q: Are the Calibration Certificates I issue affected?
A:   No, the uncertainty of measurement quoted on your certificates issued to your customers will remain unchanged as will the term “Uncertainty of Measurement”.
If the certificates you issue do, exceptionally, mention BMC then you should change the term to CMC by the end of 2010.

Q:  Can I continue to refer to BMC?
A: You should now phase out reference to BMC and replace it with CMC.  It is expected that laboratories will change any references in documents as they are reviewed, replaced or reprinted.

Q: Will customers continue to accept my certificates?
A:  Yes, this does not affect the certificates you issue which contain your Uncertainty of Measurement.  Your CMC is agreed between you and UKAS.  It describes your assessed capability achievable under near ideal conditions and with a relatively ideal artefact being calibrated.  Your certificates are not affected as they show the uncertainty of measurement for the calibration involved.  Your customers, testing laboratories and others such as product certification bodies should find this change wholly acceptable and should note that your assessed capability is unchanged.  All EA Accreditation Bodies are changing the terminology by end 2010.