Editing Metrology (section)

=== Standards ===
{{see also|Measurement#Standards}}

A [[Standard (metrology)|standard]] (or etalon) is an object, system, or experiment with a defined relationship to a unit of measurement of a physical quantity.<ref>Phillip Ostwald,Jairo Muñoz, ''Manufacturing Processes and Systems (9th Edition)''John Wiley & Sons, 1997 {{ISBN|978-0-471-04741-4}} page 616</ref> Standards are the fundamental reference for a system of weights and measures by realising, preserving, or reproducing a unit against which measuring devices can be compared.<ref name=FCM/> There are three levels of standards in the hierarchy of metrology: primary, secondary, and working standards.<ref name="silva">{{cite book|last1=de Silva|first1=G. M. S|title=Basic Metrology for ISO 9000 Certification|date=2012|publisher=Routledge|location=Oxford|isbn=978-1-136-42720-6|pages=12–13|edition=Online-Ausg.|url=https://books.google.com/books?id=0akABAAAQBAJ&q=standards+hierarchy+metrology&pg=PA13|access-date=17 February 2017|url-status=live|archive-url=https://web.archive.org/web/20180227045858/https://books.google.com/books?id=0akABAAAQBAJ&pg=PA13&lpg=PA13&dq=standards+hierarchy+metrology&source=bl&ots=VMyW0MPSAL&sig=kziWErFv0k_dtc-EjphSzdVjV_8&hl=en&sa=X&ved=0ahUKEwjW3tzX_5fSAhVh6IMKHR2RCoUQ6AEIfTAU#v=onepage&q=standards%20hierarchy%20metrology&f=false|archive-date=27 February 2018}}</ref> Primary standards (the highest quality) do not reference any other standards. Secondary standards are calibrated with reference to a primary standard. Working standards, used to calibrate (or check) measuring instruments or other material measures, are calibrated with respect to secondary standards. The hierarchy preserves the quality of the higher standards.<ref name = "silva"/> An example of a standard would be [[gauge blocks]] for length. A gauge block is a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart.<ref>{{cite web|last1=Doiron|first1=Ted|last2=Beers|first2=John|title=The Gauge Block Handbook|url=https://www.nist.gov/sites/default/files/documents/calibrations/mono180.pdf|publisher=NIST|access-date=23 March 2018}}</ref> The length of the path of light in vacuum during a time interval of 1/299,792,458 of a second is embodied in an artefact standard such as a gauge block; this gauge block is then a primary standard which can be used to calibrate secondary standards through mechanical comparators.<ref>{{cite web|title=e-Handbook of Statistical Methods|url=https://www.itl.nist.gov/div898/handbook/mpc/section3/mpc312.htm|publisher=NIST/SEMATECH|access-date=23 March 2018}}</ref>