The "Guide to the Expression of Uncertainty in Measurement" (commonly known as the GUM) is the definitive document on this subject. The GUM has been adopted by all major National Measurement Institutes (NMIs) and by international laboratory accreditation standards such as ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories, which is required for international laboratory accreditation; and is employed in most modern national and international documentary standards on measurement methods and technology. See Joint Committee for Guides in Metrology.