Editing Metrology (section)

=== Traceability and calibration===

[[File:Traceability Pyramid.png|thumb|upright=1.5|alt=Pyramid illustrating the relationship between traceability and calibration|Metrology traceability pyramid]]
Metrological traceability is defined as the "property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty".<ref name=VIM>{{Cite book |url= http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf |title= International vocabulary of metrology – basic and general concepts and associated terms |publisher= Joint Committee on Guides for Metrology (JCGM) |year= 2008 |edition= 3 |url-status= dead |archive-url= https://web.archive.org/web/20110110120304/http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf |archive-date= 2011-01-10 |access-date= 2014-06-13 }}</ref> It permits the comparison of measurements, whether the result is compared to the previous result in the same laboratory, a measurement result a year ago, or to the result of a measurement performed anywhere else in the world.<ref name=WMO>{{cite web|title=Metrological Traceability for Meteorology|url=https://www.wmo.int/pages/prog/www/IMOP/publications/Flyers/Traceability_flyer.pdf|publisher=World Meteorological Organization Commission for Instruments and Methods of Observation|access-date=2 March 2017|url-status=live|archive-url=https://web.archive.org/web/20170317094030/http://www.wmo.int/pages/prog/www/IMOP/publications/Flyers/Traceability_flyer.pdf|archive-date=17 March 2017}}</ref> The chain of traceability allows any measurement to be referenced to higher levels of measurements back to the original definition of the unit.<ref name=FCM/>

Traceability is obtained directly through [[calibration]], establishing the relationship between an indication on a standard traceable measuring instrument and the value of the comparator (or comparative measuring instrument). The process will determine the measurement value and uncertainty of the device that is being calibrated (the comparator) and create a traceability link to the measurement standard.<ref name = VIM/> The four primary reasons for calibrations are to provide traceability, to ensure that the instrument (or standard) is consistent with other measurements, to determine accuracy, and to establish reliability.<ref name=FCM/> Traceability works as a pyramid, at the top level there is the international standards, which beholds the world's standards. The next level is the national Metrology institutes that have primary standards that are traceable to the international standards. The national Metrology institutes standards are used to establish a traceable link to local laboratory standards, these laboratory standards are then used to establish a traceable link to industry and testing laboratories. Through these subsequent calibrations between national metrology institutes, calibration laboratories, and industry and testing laboratories the realisation of the unit definition is propagated down through the pyramid.<ref name=WMO/> The traceability chain works upwards from the bottom of the pyramid, where measurements done by industry and testing laboratories can be directly related to the unit definition at the top through the traceability chain created by calibration.<ref name = BGtoM/>