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--- articles:nist_traceability [2019/05/25 12:15] – [What are "International Standards"?] rrandall
+++ articles:nist_traceability [2019/05/25 12:20] – [What are SI Units?] rrandall
@@ Line 72: / Line 72: @@
 SI Units are also explained on the NIST web site at: https://www.nist.gov/pml/weights-and-measures/metric-si/si-units
-Alternatively, SI Units are also discussed in "[[https://www.nist.gov/pml/special-publication-330|NIST Special Publication 330 -  The International System of Units (SI)]]" (which will likely be updated since a significant update to the SI went into effect on May 20, 2019).
+Alternatively, SI Units are also discussed in "[[https://www.nist.gov/pml/special-publication-330|NIST Special Publication 330 -  The International System of Units (SI)]]"; which will likely be updated since a significant update to the SI went into effect on May 20, 2019. The new definitions impact four of the base units:
+  * The kilogram – will be defined in terms of the Planck constant (h)
+  * The ampere – will be defined in terms of the elementary charge (e)
+  * The kelvin – will be defined in terms of the Boltzmann constant (k)
+  * The mole – will be defined in terms of the Avogadro constant (NA)
 Because SI units are derived from intrinsic (i.e., invariant) constants of nature, "intrinsic measurement standards" exist. This is acknowledged in ISO 17025:2017, sec. 6.5.2, which provides 3 (three) different methodologies for achieving metrological traceability. And is further clarified in ISO 17025:2017, "Annex A: Metrological traceability". \\