The traceability of a measurement result refers to metrological traceability as defined by VIM. It relates the result to SI units or other agreed standards/references. Traceability is essential for comparability of analytical results and it is a strong requirement of ISO/IEC 17025. Traceability is achieved following good laboratory practice for. However it may be time consuming and expensive to calibrate all equipment. By time a laboratory should review its calibration and for stable equipment the calibration interval maybe extended by introducing control of status.
From Eurachem there is a Traceability guide and a leaflet. There is also a guide on Selection of reference materials. The picture below is from the leaflet
Example of traceability to the SI - Temperature
The temperature of a sample can be traced back through a chain of calibrations to the reference, an SI value of temperature at 0 °C. Drawing by Douglas Hasbun, Sweden.
FAQ
1 Is a SRM from NIST a CRM (Certified Reference Material)? Yes! The terms Standard Reference Material is used by NIST for a long time.
2 What is needed for a material to be a CRM? Pls refer to Eurachem guide on Reference material. Important is that the certificate clearly indicate the traceability chain. A statement Traceable to the SI ( a NIST material) needs to have information of the metrological traceability chain to the SI ( or indicate which NIST material)..