{"id":1923,"date":"2019-02-04T22:26:06","date_gmt":"2019-02-04T22:26:06","guid":{"rendered":"https:\/\/aviantechnologies.a2hosted.com\/aviantech\/?p=1923"},"modified":"2019-11-12T18:27:00","modified_gmt":"2019-11-12T18:27:00","slug":"white-paper-traceability-what-is-it-why-should-you-care","status":"publish","type":"post","link":"https:\/\/aviantechnologies.com\/avianmirror\/2019\/02\/04\/white-paper-traceability-what-is-it-why-should-you-care\/","title":{"rendered":"White Paper: Traceability – What is it? Why should you care?"},"content":{"rendered":"
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Download this white paper in PDF format<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n

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In the United States1<\/a><\/sup>,<\/a> the ultimate authority on measurement practice lies within the Department of Commerce, at the National Institute of Standards and Technology (NIST) [1]<\/a>. So to start any discussion about traceability, we should start there. NIST states that the “traceability of measurement requires the establishment of an unbroken chain of comparisons to stated references each with a stated uncertainty.”<\/p>\n

\"TraceabilityThus, traceability quite literally means the ability to be traced. \u00a0<\/em>Just like breadcrumbs leading you back to the place you started, the unbroken chain<\/em> leads you back to the original reference measurement, and in the US, those measurements are carried out at NIST. So each traceable standard has a chain of measurements connecting it to measurements performed at NIST. Further, to be traceable, the documentation accompanying the traceable standard (its certificate<\/em>) must state<\/em> how the standard is connected back to NIST. Often certificates will only list one \u201clink\u201d in the chain. Assuming all of the previous links are trustworthy, one link is all that is really required to continue the chain. End users almost never continue this chain, but others will. For example, Avian Technologies, and other measurement services organizations by definition are providing physical standards and traceable measurements, each with a connection to the chain back to NIST. Often larger companies will also perform additional transfer measurements.<\/p>\n

In summary, traceability requires a defined connection between any traceable standard, upstream through a series of measurements, ultimately ending at a reference measurement performed at an NMI.\u00a0 The position along the chain may carry special meaning, and therefore deserves special terminology. Standards that have been directly measured by an NMI are called primary standards<\/em>. Avian Technology maintains many primary standards, as should any measurement services organization. After primary standards, the specific definitions get a little fuzzy; often the next level below primary is secondary standard<\/em>, and after that, transfer standard<\/em>. The end user has a working standard<\/em> daily as a part of a measurement program. A standard that is supplied with a commercial instrument is an example of a working standard.<\/p>\n

Now that we have a general idea of what traceability is and before going further, we need to understand what traceability is Not<\/strong>?<\/h4>\n

Laboratories who are contracting for measurement services want assurances of traceability, but they generally believe that traceability implies accuracy or implies that the measurement laboratory maintains ISO (9001 or 17025) certification.<\/p>\n

Unfortunately, neither is necessarily true. There is no mention of accuracy in the NIST definition of traceability.\u00a0 While we at Avian Technologies strive for the most accurate measurements possible, this alone does not ensure, or even imply, traceability.\u00a0 ISO certification is a process that laboratories may choose to undergo.\u00a0 The certification states that they have and maintain certain procedural criteria in their workplace.\u00a0 Again, this does not necessarily equate to either accuracy or traceability.<\/p>\n

What then is the process of producing a traceable standard?<\/h4>\n

A client ordering a traceable standard will receive a physical standard and a certificate.\u00a0 The certificate will contain the results of measurements performed on the standard, for example values of reflectance measured over a range of wavelengths.\u00a0 The certificate will also state uncertainties for the measurements (original statement from NIST, \u201ceach with a stated uncertainty\u201d).\u00a0\u00a0 The quantity that is stated for each wavelength is called the measurand and is the quantity that we seek, for example spectral reflectance or color coordinates.\u00a0 The uncertainty is \u201cthat parameter, associated with the result of measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand\u201d (from the ISO guidelines to the expression of uncertainly in measurement, hereafter referred to as GUM).\u00a0 The uncertainty is what is transferred between instruments and each instrument has a stated uncertainty.<\/p>\n

As commonly defined and used, \u201cuncertainty\u201d means the lack of a precise understanding of something. The relevant definition of uncertain<\/em> from Merriam-Webster lists three related phrases:<\/p>\n