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Cite this document
Precision and accuracy are two concepts of statistical characterization of a process. Precision concerns the spread between the individual measurements in the process, whereas accuracy concerns the deviation of such measurements from an accepted reference level for the property or characteristic measured. An accurate process is also precise, but a precise process is not necessarily accurate. Generally, the index of accuracy will consist of two or more different numbers. Since the concept of accuracy embraces not only the concept of precision, but also the idea of more or less consistent deviation from the reference level (systematic error or bias), it is preferable to describe accuracy by separate values indicating precision and bias. For further information, the reader is referred to the ASTM Recommended Practice for Use of the Terms Precision and Accuracy as Applied to Measurement of a Property of a Material (E 177-71).