Classification of Standards and Gauge Control Structure
The accuracy in a vast industrial complex can be maintained only if its standards are traceable to a single source ,usually the
Fig. 3.10. Movement of carriage is required (not absolute method.) National Standard of the country, which are further linked up with International Standards. Fig. 3.11 explains how the accuracy of maesurement is transferred from National Standards to the working shop floor standards.
Since frequent use may impair the accuracy of any standard, direct comparisons with National Standards are less frequently performed. In such a case, a slightly lower order of standards, known as National Reference Standards are used. Working standards are ordinarily used in calibration work. These are compared as frequently as necessary with National Reference Standards.
Clearly, there is a degradation of accuracy in passing from the defining standards to the standards in use. The accuracy of a particular standard depends on a combination of the number of times it has been compared with a standard in a higher echelon, the recentness of such comparisons, the care with which it was done, and the stability of the particular standard itself.