What is the difference between traceable and accredited calibration

When discussing calibration, two terms are often encountered: traceable calibration and accredited calibration. They may sound similar, but their meaning, level of assurance, and use cases differ. Understanding the difference is essential when measuring instruments are used for production quality assurance, demonstrating conformity, or risk management.

Traceable calibration

The traceability of a measurement result is defined in the International Vocabulary of Metrology (VIM) as follows: a measurement result is traceable when it can be linked, through an unbroken and documented calibration chain, to an agreed reference. Typically, the reference used is the SI system of units. Every additional link in the chain increases measurement uncertainty.
In practice, this means that:

• the measuring instrument has been calibrated against a reference standard
• the reference standard has its own calibration
• the chain extends to a national or international measurement standard
• documentation exists for the calibration

Traceable calibration does not, in itself, specify who performs the calibration or at what competence level, as long as the traceability chain exists and can be verified. Nor does it automatically mean that measurement uncertainty has been calculated in accordance with standards or that the methods have been externally assessed.

Traceable calibration may be entirely sufficient, for example, for internal monitoring, non-critical production stages, or reference measurements where the risk is controlled.

Accredited calibration

Accredited calibration is always traceable, but the reverse is not true. In accredited calibration, an independent national accreditation body—in Finland, FINAS—has assessed and verified that the calibration laboratory meets the requirements of ISO/IEC 17025. An accredited laboratory is technically competent specifically for the measurements defined within its scope of accreditation. Such a laboratory controls the calculation of measurement uncertainty, uses approved methods, operates under controlled and documented conditions, and is subject to continuous external assessment.

In an accredited calibration certificate, measurement uncertainty is stated in accordance with the standard, traceability is externally verified, and both the content and format of the certificate are suitable for audits.

Accredited calibration is typically required in situations where:

• measurement results are used to demonstrate conformity
• the results have safety, regulatory, or contractual significance
• operations are subject to certifications, regulatory requirements, or standards
• customers or auditors require accreditation

This table presents the key differences between traceable and accredited calibration:

Who is responsible?

The purpose of calibration is not to approve or reject results; it only establishes the condition of the measuring instrument at the time of calibration. Whether traceable calibration is sufficient or accredited calibration is required always depends on the instrument’s intended use and a risk-based assessment. The choice forms part of the company’s own quality management system.

The owner of the measuring instrument always makes the final decision on whether to put the device into use—the calibration certificate provides a factual basis for that decision.

Would you like to hear more about calibration?

SGS provides expert calibration services for a wide range of measuring instrument types, including general measurement technology, data networks, wireless communications, radio frequency technology, fibre optics and EMC testing equipment. We offer a broad accredited*) calibration scope and carry out calibrations not only in our own laboratory, but also at customer premises.

Contact us.

*)SGS Fimko Oy’s calibration laboratory is a calibration laboratory accredited by the FINAS accreditation service, K001, with EN ISO/IEC 17025 as the accreditation requirement.