This standard lays down the principles for the classification of measuring instruments according to their accuracy. 1.1.2 The measuring instruments to which this standard applies are: - material measures, - measuring instruments, - measuring transducers, where these instruments are intended for use in conditions in which errors due to inertia are negligible in relation to the maximum errors laid down for them. 1.1.3 The requirements of this standard are not mandatory for zero indicating instruments, or for equipment especially designed for measuring by multiple reading of the indications and for determining the measurement results as the arithmetic mean of several observations. The standard does not apply to measuring instruments intended to reproduce, convert or measure quantities linked simultaneously to several parameters, if different maximum errors have to be fixed for these instruments (eg measurement generators, cathode ray oscilloscopes) in accordance with these parameters. 1.2 Principles of classification according to accuracy 1.2.1 The classification of measuring instruments according to their accuracy is to be effected by drawing up classes characterizing different levels of accuracy for instruments of the same category. For each accuracy class of one category of instruments, the parameters and characteristics, which determine the particular metrological properties and could cause instrument errors in the measurements carried out with these instruments, must be fixed. For each category of instruments, a certain number of accuracy classes must be fixed reflecting those levels of metrological properties which correspond to established requirements of science and technology. Note: The index attributed to a particular accuracy class reflects a certain general level of metrological properties in the instrument but does not directly indicate the accuracy of measurements made with this instrument. 1.2.2 The parameters and characteristics of measuring instruments used when classifying them according to their accuracy are: - intrinsic error, - complementary error, caused by variations in the influence quantities, which appears in the variation of the indications of the measuring instruments, in the variation of the quantity reproduced by the material measures or in the variation of the metrological characteristics of the measuring transducers, - instability with time, - hysteresis error, and - other properties affecting the accuracy of the instruments. Examples: The parameters and the metrological characteristics are: - for end gauges: the difference between their real length and their nominal length, the admissible deviation in the flatness and parallelism of their measuring faces, the wringing and instability with time, - for standard cells: instability with time, - for electrical indicating measuring instruments: the intrinsic error and the variations in the indications caused by specified changes of the influence quantities (temperature, frequency of alternating current, etc), - for weighing instruments: the intrinsic error, the hysteresis error, the levelling error. 1.2.3 The parameters and the characteristics defining the metrological properties of measuring instruments and the concrete values of these parameters and characteristics must be fixed in the GS and in the national statutory documents relating to general technical requirements to be satisfied by the instruments of the categories in question, depending on the principle of operation of these instruments, their construction, their intended use and their working conditions. 1.2.4 The parameters and the characteristics peculiar to each category of instruments are given in the form of maximum permissible intrinsic and complementary errors (or, instead of these, of variations in the indications caused by variations of the special influence quantities), of maximum permissible instability and of maximum permissible deviations from a reference value for other metrological properties. 1.2.5 With a view to fixing the accuracy classes for measuring instruments, the maximum errors and the norms must be established according to the methods, and be expressed in one of the forms given in clause 4 of this standard*. 1.2.6 The series of accuracy classes and their connection with the corresponding maximum errors must comply with the provisions in clause 5 of this standard. 1.2.7 The indices of accuracy classes used in standard and statutory documents and marked on the instruments must correspond to those laid down in clause 6 of this standard. 1.2.8 The test to determine the conformity of the measuring instruments with their accuracy class must be carried out by determining each of the parameters and each of the characteristics separately.