A certified reference material is a substance produced with a precisely known composition for a specific property, with an accompanying uncertainty and documentation. Analysts use it to verify that their measurement method is accurate and to assess precision. In practice, you treat a CRM like a real sample, measure its value, and compare what you obtain to the certified value. If the result falls within the expected uncertainty, the method is performing correctly; if not, it signals a potential issue with calibration, sample prep, or instrumentation that needs addressing. CRMs are chosen to resemble the sample matrix to ensure the test conditions are realistic and to establish traceability to standard references. For example, using a CRM with a certified gold concentration in a rock-like matrix lets you confirm that your assay method yields the right result with known uncertainty.