= Reference material
A \b[reference material] is established as suitable for a specified measurement use because the relevant properties are sufficiently homogeneous and stable. The requirement concerns particular properties and an intended use, rather than every possible attribute of the material.<International vocabulary of metrology by JCGM>[VIM3entry5.13, definition]{ref} <Reference material homogeneity> concerns variation within or between the portions used; <reference material stability> concerns maintaining the relevant properties over time and under stated conditions.
Reference materials can support <measurement precision> control even without an assigned quantity value. An assigned value is needed when the material serves in <measurement calibration> or a check of <measurement trueness>.<International vocabulary of metrology by JCGM>[Entry5.13, note2]{ref} A <certified reference material> adds authoritative documentation specifying property values with associated uncertainties and traceabilities obtained through valid procedures.<International vocabulary of metrology by JCGM>[Entry5.14, definition]{ref}
A concrete physical example is the archived 2009 certificate for <National Institute of Standards and Technology> SRM 1922, a mineral oil characterized for <refractive index>. Its characterization used a precision <spectrometer> and <goniometer> arrangement with the <minimum deviation> method, oil in a hollow <optical prism>, and water-bath temperature control. Measurements covered several wavelengths and temperatures; multiple portions were examined to assess homogeneity.<Certificate for Standard Reference Material 1922 by National Institute of Standards and Technology>[Certificate issued 24 June 2009, p1, Certified Values and Uncertainties]{ref}
The certificate's Table 1 reports, at wavelength 589.3 nm and temperature $20\,{}^\circ\mathrm C$, refractive index 1.46945 with <expanded uncertainty> $6\times10^{-5}$ and <coverage factor> 2. This wavelength's value was obtained through a dispersion fit. The listed temperature coefficient is $-3.68\times10^{-4}\,\mathrm{K^{-1}}$.<Certificate for Standard Reference Material 1922 by National Institute of Standards and Technology>[p1, fitted 589.3nm values and coverage factor; p2, Table1]{ref}
An original calculation using that linear coefficient predicts
$$
n(22\,{}^\circ\mathrm C)
\simeq1.46945+
(-3.68\times10^{-4}\,\mathrm{K^{-1}})(2\,\mathrm K)
=1.468714.
$$
The predicted change, $0.000736$ in magnitude, is larger than the quoted expanded uncertainty at the reference conditions. Temperature therefore belongs with the assigned optical value; it is not an incidental label. This calculation illustrates the certificate's model, rather than supplying a new certified value or uncertainty.
Record the material identity, certificate version, property, wavelength, temperature and handling history with a measurement result. The archived certificate supplies a documented example of those links, rather than a claim about a currently available product or the validity of a particular bottle today.
Back to article page
