What the Move to CMC Means for Accredited Labs
Metrological traceability provides reliability in measurements
around the world. It is transferred via calibration
laboratories accredited by signatories to the International
Laboratory Accreditation Cooperation (ILAC) Mutual Recognition
Arrangement (MRA) and by National Metrology Institutes (NMIs) -
such as the National Institute of Standards and Technology (NIST) -
under the International Committee of Weights and Measures (CIPM)
MRA. Currently, the services provided by many accredited
calibration laboratories are described using the term "Best
Measurement Capability" (BMC). This terminology is in widespread
use in accreditation programs around the world.
Currently, the services provided by many accredited calibration
laboratories are described using the term "Best Measurement
Capability" (BMC). This terminology is in widespread use in
accreditation programs around the world.
NMIs have a similar description of the services provided to
their customers, but use the term "Calibration and Measurement
Capability" (CMC).
Change of Terminology
To address this inconsistency in terminology, the International
Bureau of Weights and Measures (BIPM) and the regional metrology
organizations (RMOs) have, in cooperation with ILAC and the
regional (accreditation) cooperation bodies, arrived at the
following conclusion:
"In the context of the CIPM MRA and ILAC Arrangement, and in
relation to the CIPM-ILAC Common Statement, the following shared
definition is agreed upon:
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."
This means that BMC and CMC shall be considered equal by
accreditation bodies, laboratories, their customers, the market and
regulators.
ILAC has therefore decided to make a change in terminology and
in the future all references to BMC will be changed to CMC (see
ILAC 2009-08-20 BMC to CMC Circular).
Implications for Accredited Calibration
Labs
The current uncertainty of measurement quoted on your
calibration certificates or reports will remain unchanged as a
result of this change in terminology. If, however, you currently
use the term BMC on your calibration certificates or other
documentation, this will need to be changed to CMC. (Note: The term
"uncertainty of measurement" remains unchanged.)
ACLASS has already begun changing this terminology on its scopes
of accreditation and expects to complete the process in the next
few months. It is being done as each calibration laboratory is
assessed or when their scope of accreditation is revised, whichever
comes first.
Greater Harmonization
The intent of this change is to achieve worldwide harmonization
of terminology in dissemination of metrological traceability. Use
of the same terminology by accredited calibration laboratories and
NMIs will greatly assist progress toward this goal and help provide
clarity in the marketplace.
While this terminology change will improve the dissemination of
metrological traceability throughout the world, the ongoing
technical issues relating to measurement capability (for example,
contribution from device under test to the measurement uncertainty)
continue to be addressed in conjunction with BIPM. ILAC policy
documents on these issues will be published in the future.
Further Information
• ILAC 2009-08-20_BMC to CMC Circular is at
http://www.ilac.org/publicationsandresources.html
• Calibration and Measurement Capabilities - a Paper by the
Joint BIPM/ILAC working group available at
http://www.ilac.org/publicationsandresources.html
Contact Details
For more information, please call 703-836-0025 to speak with
Terry Burgess, ext. 225.
Notice for Customers of Calibration
Services
The calibration certificates and reports you receive should
still be accepted even though there may have been a change in
terminology from BMC to CMC. The source of traceability, technical
competence, and capability of the calibration laboratories, as
assessed by the accreditation bodies, has not changed as a result
of this change in terminology.
ACLASS-accredited laboratories are encouraged to share this
information with their customers and include appropriate contact
information (laboratory address, contact number, e-mail address,
etc.)