The term "traceability" describes a process through which a measurement taken by a measuring instrument can be compared, in one or more steps, with a national standard for the physical value.
These steps must form an uninterrupted chain of calibrations. In each step, a measuring instrument is compared with a standard whosemeasurement features themselves have been determined by comparison with a higher ranking standard. This process creates a calibration hierarchy or a hierarchy of the testing equipment. The bodies performing the comparisons within the chain must also have their technical expertise verified, e.g. through accreditation by a calibration authority.
Calibrations performed by other bodies not accredited as calibration authorities are not considered traceable in line with EN ISO 9001 or EN ISO/IEC 17025 (even if they hold certification in accordance with this standard),as in this case, the body's technical expertise is not proven.