What is metrological traceability and how is it established?

Metrological traceability is an unbroken chain of comparisons linking a measurement to national/international standards. Requirements per ISO/IEC 17025: documented unbroken chain to SI units or accepted references, stated measurement uncertainty at each step, documented procedures, technically competent laboratory (often accredited), recalibration at appropriate intervals, and records maintained. National Metrology Institutes (NIST, PTB, NPL) maintain primary standards. Working standards are calibrated against reference standards, which trace to national standards. Each calibration adds uncertainty. Traceability ensures measurement comparability worldwide and is essential for legal metrology and quality systems.