In calibration of support equipment, the values realized by standards are established through the use of reference standards that are traceable to the International System of Units (SI).
In calibration according to methods, the values realized by standards are typically established through the use of reference materials that are either purchased by the laboratory with a certificate of analysis or purity, or prepared by the laboratory using support equipment that has been calibrated or verified to meet specifications.
06-096 C.M.R. ch. 263, § 2