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In the United States, and other countries throughout the world, the National
Metrology Institutes are usually not the sole supplier of the needed reference
standards for that country. Normally, secondary calibration laboratories
produce and calibrate the majority of test blocks for use by industry. Whereas,
NIST is planning to only provide test blocks for three hardness levels of
each Rockwell scale, the secondary calibration laboratories usually provide
reference blocks at multiple hardness levels, allowing a better verification for
a specific level of hardness.
The secondary calibration laboratories are linked to the national Rockwell
scales through the use of primary reference standards to calibrate their
standardizing machines and, often, through some form of accuracy assurance
program in connection with the primary standardization laboratory (NMI).
In the United States, this is accomplished through direct verification of the
secondary laboratories’ standardizing machines using NIST traceable
instruments and artifacts, indirect verification of the secondary laboratories’
standardizing machines using NIST SRM test block standards, and voluntary
participation in a calibration laboratory accreditation program. Because NIST
SRMs are currently available only for the Rockwell C scale, the secondary
reference test blocks of other Rockwell scales cannot be calibrated traceable
to NIST Rockwell scales.
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