This process of extending calibration is called metrological traceability.

These institutes, whose activities are peer-reviewed, provide the top-level reference points for metrological traceability.

The use of metrological traceability to connect different regimes of measurement is similar to the idea behind the cosmic distance ladder for different ranges of astronomical length.

Certified Reference Materials (CRMs) are 'controls' or standards used to check the quality and metrological traceability of products, to validate analytical measurement methods, or for the calibration of instruments.

These units are then established and maintained through various agencies in each country, and establish a hierarchy of measurement standards that can be traced back to the established standard unit, a concept known as metrological traceability.

Reference material characterized by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability.

Recent attention has been given to forensic metrology and metrological traceability as a result of an international effort to accredit forensic laboratories and criminalistic laboratories to the International Organization for Standardization 17025 requirements.

Metrological traceability permits comparison of measurements, whether the result is compared to the previous result in the same laboratory, a measurement result a year ago, or to the result of a measurement performed anywhere else in the world.

Quality management systems involving laboratory accreditation under national and international accreditation/certification standards such as ISO/IEC 17025 require metrological traceability to Certified Reference Materials (where possible) when using reference materials for calibration.

Calibration laboratories and proficiency testing schemes Calibration laboratories provide legal metrological traceability in South Africa as stipulated in the Measurements Units and Measurement Standards Act (Act No. 18 of 2006).

Reference Materials that do not meet all the criteria for certified reference materials are more widely available: the principal difference is the additional evidence of metrological traceability and statement of measurement uncertainty provided on the certificate for certified reference materials.

This new OptiQuant HIV Panel fully complies with the ISO 17511:2003 (In vitro diagnostic medical devices -- Measurement of quantities in biological samples -- Metrological traceability of values assigned to calibrators and control materials) standard.

A core concept in metrology is metrological traceability, defined by the Joint Committee for Guides in Metrology as "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".