For those measurement parameters where it is available, participation is mandatory in an appropriately rigorous PT (testing at the level of the laboratory’s accredited capabilities).

NVLAP accepts proficiency test results from an accredited laboratory when:

a) The PT provider is accredited to ISO/IEC 17043 for the parameter being tested at the uncertainty level of that test, and that the accreditation to ISO/IEC 17043 is issued by a body which is signatory to a mutual recognition arrangement (MRA) for proficiency testing accreditation in a regional body recognized by the International Laboratory Accreditation Cooperation (ILAC).

b) The PT is coordinated through the NIST Office of Weights and Measures (OWM) Regional Measurement Assurance Program (RMAP)

c)The PT or Measurement Assurance Program (MAP) is offered through a NIST technical division.

See the current version of NIST Handbook 150-2 for additional guidance.