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118 Part II: Metrology
International standards
National standards
Primary standards
Secondary standards
Reference standards
Working standards
Part II.F.2
Transfer standards
Figure 12.2 Calibration standards hierarchy.
• Secondary standards. A standard whose value is based on comparisons
with some primary standard. Note that a secondary standard, once
its value is established, can become a primary standard for some
other user.
• Reference standards. A standard having the highest metrological quality
available at a given location, from which the measurements made at
that location are derived.
• Working standards. A measurement standard not specifically reserved
as a reference standard, that is intended to verify measurement
equipment of lower accuracy.
• Transfer standards. A standard that is the same as a reference standard
except that it is used to transfer a measurement parameter from one
organization to another for traceability purposes.
In order to maintain accuracy, standards in industrialized nations must be
traceable to a single source, usually the country’s national standards. Since the
national laboratories of industrialized nations maintain close connections with
the International Bureau of Weights and Measures, there is assurance that items
produced under calibration standards in one country will be consistent with
items produced under calibration standards in other countries.