Measurement Traceability in Practice: How Results Become Comparable Across Laboratories

Measurement traceability allows a result to be related to a recognised reference through a documented and unbroken chain of calibrations. Each link contributes to measurement uncertainty. Traceability makes results more comparable, but it does not mean that every result is correct or suitable for its purpose. This working paper explains traceability in plain language. It describes the connection to the International System of Units, the role of national metrology institutes and calibration laboratories, the information that should appear in calibration records, and the common ways in which a traceability chain can fail. Examples from medical metrology show how the principle works in practice. The main conclusion is that traceability is not a logo or a certificate alone. It is a complete body of technical evidence.