Ensuring Accuracy and Traceability of Weighing Instruments (by Georgia Harris): Operators of weighing devices must have confidence in the accuracy and traceability of their weighing equipment. To develop this confidence, they need to be able to evaluate scale and balance service companies and calibration organizations that they engage. Assurance of accuracy and traceability are the two most important factors in characterizing the quality of measurement results. Measurement quality is partially determined by, and critically dependent on, these two vital factors. Defining Accuracy and Traceability- The following definitions are published by the International Organization for Standardization (ISO) in the International Vocabulary of Basic and General Terms In Metrology, 1984. Accuracy The closeness of the agreement between the result of a measurement and the (conventional) true value of the measurand. Or, the ability of a measuring instrument to give indications approaching the true value of a measurand. In simple terms, Accuracy refers to whether or not a measurement is correct, free from error, and reflects the true value. ASTM standard E 456, Terminology Relating to Quality and Statistics, defines “Accuracy” as “the closeness of agreement between a test result and an accepted reference value.” Since nothing is ever perfect, We estimate by repeated measurements, how close our measurements are to the true values. This is critical for assessing accuracy. Traceability-The property of a result of a measurement whereby it can be related to appropriate standards, generally international or national standards, through an unbroken chain of comparisons. Traceability implies an ability to relate individual measurement results through an unbroken chain of calibrations to a common source. In the United States, this ultimately leads back to national standards maintained by the National Institute of Standards and Technology (NIST). This unbroken chain constitutes an “audit trail.” To support a claim of traceability, an adequate audit trail must be established using documentation. This documentation provides acceptable evidence that becomes important when using calibration services and when evaluating the traceability of test weights used to establish the accuracy of weighing equipment.