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--- articles:nist_traceability [2019/01/26 14:41] – [An "unbroken chain of calibrations" to what?] rrandall
+++ articles:nist_traceability [2019/05/25 12:20] – [What are SI Units?] rrandall
@@ Line 41: / Line 41: @@
 a. calibrated or verified, or both, at specified intervals, or prior to use, against measurement standards __traceable to international or national measurement standards; when no such standards exist, the basis used for calibration or verification shall be retained as documented information__;//"
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-Unfortunately, the language in ISO 9001:2015 & AS9100:2016 (Rev. D) is extremely antiquated (by 55 years) in stating its requirements for "measurement traceability". In contrast, ISO 17025:2017 is much more modern and technically correct in stating:\\
+Unfortunately, the language in ISO 9001:2015 & AS9100:2016 (Rev. D) is extremely antiquated in stating its requirements for "measurement traceability". In contrast, ISO 17025:2017 is much more modern and technically correct in stating:\\
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 **ISO 17025:2017, “General requirements for the competence of testing and calibration laboratories”** \\
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 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. 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". \\
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 While ISO 9001:2015, AS9100:2016 (Rev. D) and ISO 17025:2017 all mention "International Standards", I am aware of only four (4) "international standards" (as opposed to SI //units//); three of which are listed as examples in the "Bureau International des Poids et Mesures" (BIPM) [[https://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf|JCGM 200:2012, "International vocabulary of metrology – Basic and general concepts and associated terms (VIM)"]] (3rd edition), sec. 5.2, "international measurement standard". However, there are probably others. Those that I am aware of include: \\
 \\
-**1 - The international prototype of the kilogram** \\
+**1 - The international prototype of the kilogram (OBSOLETE as of May 20, 2019)** \\
 All of the SI units are based on physical constants of nature EXCEPT the kilogram. The kilogram is the unit of mass; which nominally has the same mass as one litre of water at the freezing point.
 The only SI unit "physical artifact" (i.e., not defined by a fundamental, natural constant), the international prototype kilogram (IPK), was certified in 1889, and consists of a cylinder of platinum-iridium. The IPK is maintained by the [[https://www.bipm.org/en/publications/si-brochure/kilogram.html|BIPM]].
-<note>Because the IPKs stability has been a matter of significant concern, during November 2018, the world’s measurement experts voted and unanimously approved a revision of the SI that establishes a measurement system entirely based on physical constants of nature. The changes will take effect on [[http://www.worldmetrologyday.org|World Metrology Day]], May 20, 2019. See [[https://www.theverge.com/2018/11/13/18087002/kilogram-new-definition-kg-metric-unit-ipk-measurement|The Kilogram is Dead; Long Live the Kilogram]]</note>
+<note>Because the IPKs stability has been a matter of significant concern, during November 2018, the world’s measurement experts voted and unanimously approved a revision of the SI that establishes a measurement system entirely based on physical constants of nature. The changes took effect on [[http://www.worldmetrologyday.org|World Metrology Day]], May 20, 2019; which  commemorates the anniversary of the signing of the Metre Convention in 1875. See [[https://www.theverge.com/2018/11/13/18087002/kilogram-new-definition-kg-metric-unit-ipk-measurement|The Kilogram is Dead; Long Live the Kilogram]]</note>
 **2 - Chorionic Gonadotrophin (Biological standard)** \\
 Defined by the [[http://apps.who.int/iris/bitstream/handle/10665/70154/WHO_BS_09.2107_eng.pdf|World Health Organization (WHO)]] in the 4th international standard 1999, as 75/589, 650 International Units per ampoule.