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.