ISO 17025 is an International Standard and grew out of ISO Guide 25. In 2002 ISO started assessing all calibration labs to 17025. It has been updated several times since then, cleaning ambiguities, strengthening traceability requirements and expanding its overall coverage of processes. The premise of ISO 17025 is that traceability and a fully developed uncertainty statement are required to establish confidence in the calibration. Traceability is required to SI Standards (international standards based on the new SI units of measure). ISO 17025 also requires a full total uncertainty statement for the laboratory to prove the accuracy of the calibration. Its procedures assess the training and competencies of the lab personnel and the calibration procedures. ISO 17025 also requires accreditation by an internationally recognized authority.