This short module strengthens your foundations in measurement uncertainty (MU). You will explore key VIM definitions, including traceability and its link to MU. We clarify what measurement uncertainty is, and why it is different to errors. You will learn how decision rules support statements of conformance under ISO/IEC 17025 and legal or regulatory contexts. We introduce the idea of measurement assurance, including QC, calibration, competence, audits and risk and the link to MU. Finally, we outline a simple process for estimating expanded uncertainty and compare top-down and bottom-up approaches.