According to the ISO/IEC Guide 99—“International vocabulary of metrology—Basic and general concepts and associated terms (VIM),” the traceability of a measurement result is demonstrated through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty. This means that not only is it necessary to use a reference standard of length that has an unbroken chain of calibrations, but the uncertainty of the resulting measurements must also include the uncertainty of all the links in the calibration chain.

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