Metrological traceability is a fundamental concept in measurement science and a key requirement of ISO/IEC 17025. It is the property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.
The Traceability Chain
Imagine a pyramid. At the very top is the definition of the SI unit, maintained by the International Bureau of Weights and Measures (BIPM). Below that are the national metrology institutes (NMIs), such as NIST in the United States or PTB in Germany. These NMIs hold the primary national standards. The traceability chain then flows down through accredited calibration laboratories to the end user.
How to Establish Traceability
For a testing laboratory, the most common way to establish traceability is by having your equipment calibrated by an accredited calibration laboratory. When you receive a calibration certificate, you should check for the following:
- Accreditation Body Logo: The certificate should bear the logo of an accreditation body that is a signatory to the ILAC Mutual Recognition Arrangement (MRA).
- Reference to ISO/IEC 17025: The certificate should state that the calibration was performed in accordance with ISO/IEC 17025.
- Statement of Traceability: The certificate should include a statement of traceability to a national or international standard.
- Measurement Uncertainty: The certificate must report the measurement uncertainty associated with the calibration.
Why it Matters
Without metrological traceability, your measurement results are just numbers. Traceability gives you confidence that your results are accurate and comparable to results from other laboratories around the world. It is the foundation of a sound quality management system.