Classification of measuring devices by their accuracy

Conclusions

It is proposed to divide the general criterion for the accuracy of measures and measuring instruments expressed by a conventional sign or number into two notations, those of accuracy categories and accuracy classes. Categories of accuracy should be assigned to such groups of measuring devices (sets of measures of various nominal values) for which it is impossible to establish a single-valued characteristic expressed in relative units or measurement units. Categories of accuracy represent a nominal characteristic and its content can only be determined by evaluating the relation between a scale of a certain grade of accuracy and the numerical parameters which determine the accuracy of measurement by means of a given device without introducing corrections. Classes of accuracy characterize devices for which a given error characterizes completely and in a single-valued manner their metrological properties.

For a more complete metrological characterization of measures and measuring instruments, it is advisable to indicate on the measures or measuring instruments, or in their certificates, in addition to their nominal categories and classes also their ranges, scale factors, or scale values.

It is possible to use a double classification system, i.e., to assign to a single measure or measuring instrument both its category and class of accuracy. It has already been pointed out that the category characterizes the degree to which a measure of measuring instrument approaches its maximum attainable accuracy with the existing technique for measuring the given physical value. The class of accuracy indicates the tolerated and actually attainable limiting measurement error.