Metrology is the science of weights and measures. Tools and support equipment sometimes require periodic calibration. CMRS is a summary of the technical requirements of an item that outlines the measurement parameters, specific ranges, and accuracy requirements to support Test Accuracy Ratio (TAR) requirements and calibration data for each echelon of measurement. It is primarily used to determine that the end item or system is adequately supported with test/measurement and calibration equipment. It also identifies the need for calibration equipment and standards, thereby documenting a traceability of measurement accuracy to the US National Institute of Standards and Technology (NIST). There is usually a four to one (or better) increase in accuracy between each category.