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ISO Guide 33:2015 describes good practice in using reference materials (RMs), and certified reference materials (CRMs) in particular, in measurement processes. These uses include the assessment of precision and trueness of measurement methods, quality control, assigning values to materials, calibration, and the establishment of conventional scales. This Guide also relates key characteristics of various types of RMs to the different applications.

For CRMs, the metrological traceability of the property values to international scales or other measurement standards has been established. For RMs not being CRMs, this kind of traceability of property values has often not been established. Nevertheless, these RMs can still be used for assessing parts of measurement procedures, including evaluating various levels of precision

Mainstream applications of RM include precision control, bias assessment, calibration, preparation of calibration RMs and maintaining conventional scales.

NOTE Not all types of RMs can be used for all indicated purposes.

The preparation of RMs for calibration is also part of the scope of ISO Guides 34 and 35. The treatment in this Guide is limited to the fundamentals of small-scale preparation of RMs and the value assignment, as used by laboratories to calibrate their equipment. Larger scale production of such RMs, with the possible aim of distribution is beyond the scope of this Guide. This type of activity is covered in ISO Guides 34 and 35.

The development of working standards, as used in, e.g. natural gas analysis, clinical chemistry, and the pharmaceutical industry is not covered in this Guide. This type of activity is covered in ISO Guides 34 and 35.