Clause 6.5: Metrological traceability

What the clause asks for

Clause 6.5 requires the laboratory to establish and maintain metrological traceability of its measurement results through a documented, unbroken chain of calibrations, each contributing to the measurement uncertainty, linking results to an appropriate reference.

Results are traceable to the International System of Units (SI) through one of three routes (6.5.2): calibration by a competent laboratory, certified values of certified reference materials from a competent producer, or direct realization of the SI units confirmed by comparison. Calibration laboratories that meet ISO/IEC 17025 are considered competent for this purpose.

Where traceability to the SI is not technically possible, the laboratory demonstrates traceability to an appropriate reference instead (6.5.3), such as certified values of reference materials or results of reference measurement procedures, methods or consensus standards that are clearly described and agreed.

Annex A of the standard gives further guidance, and your accreditation body will usually have its own traceability policy.

What assessors sample

For an instrument used in a reported result, the assessor asks for the calibration certificate and checks that the provider was accredited for that calibration (the scope, not just the logo), that the certificate states uncertainty, and that the reference standards you use in-house are themselves calibrated. Common findings:

• A provider accredited for some calibrations but not the one performed.
• Certificates without measurement uncertainty.
• In-house calibrations against reference standards whose own traceability is not recorded.
• Reference materials used past their certificate’s validity.

Where this lives in AccreditBook

Requirement	Field in AccreditBook
Competent provider (6.5.2 a)	Calibration event: performed by, provider accredited (yes or no), provider accreditation body, certificate number
Uncertainty in the chain	Calibration event: uncertainty
Certificate evidence	Certificate attached to the calibration event
In-house reference standards	Equipment with status “reference standard” and its Reference standard tab: traceability chain, nominal value, uncertainty and coverage factor, provider and certificate
Reference materials (6.5.3 a)	Reference standard tab and attached certificate

Reference standards are ordinary equipment items, so their own calibrations, due dates and certificates follow the same register and due list as everything else. The assessor pack lists the provider and accreditation details beside each calibration.

See Equipment, Calibration events and Clause 6.4.