About NIST (The National Institute of Standards and Technology)
The mission of NIST is to develop and promote measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. To help meet the measurement and standards needs of U.S. industry and the nation, NIST provides calibrations, standard reference materials, standard reference data, test methods, proficiency evaluation materials, measurement quality assurance programs, and laboratory accreditation services that assist a customer in establishing traceability of results of measurements or values of standards.
NIST traceability is a property of a measurement, not of a device (instrument). For example, you cannot have a flow meter that is traceable to NIST. You can have a calibrated flow meter whose indications are traceable to NIST, providing certain criteria have been met.
NIST traceability requires the establishment of an unbroken chain of comparisons to stated references. Traceability is characterized by the following essential elements:
- An unbroken chain of comparisons going back to stated references acceptable to the parties, usually a national or international standard;
- Uncertainty of measurement for each step in the traceability chain. Uncertainty must be calculated or estimated according to agreed methods and must be stated so that an overall uncertainty for the whole chain may be calculated or estimated;
- Documentation for each step in the chain, performed according to recognized and generally acknowledged procedures;
- Evidence of technical competence by the laboratories or bodies performing one or more steps in the chain (e.g. by demonstrating that they are accredited);
- Reference to SI units. The chain of comparisons must, where possible, end at primary standards for realization of the SI units;
- Calibrations repeated at appropriate intervals. The length in of these intervals will depend on a number of variables, such as uncertainty required, frequency of use, way of use, stability of equipment, etc.
NIST assures the traceability of results of measurements or values of standards that NIST itself provides, either directly or through an official NIST program or collaboration. Other organizations are responsible for establishing the traceability of their own results or values to those of NIST or other stated references.
To learn more, go to www.nist.gov.