An analysis of errors in the calibration of electric instruments

It has often been stated that the standards and equipment used to calibrate an electric instrument, or other electric measuring apparatus, should be ten times as accurate as the instrument being tested. This rule-of-thumb usually leads to impossible demands on the accuracy of the standards, particularly if more than two echelons of standards are involved. Troublesome problems should be expected in primary, secondary, and tertiary standardizing laboratories in large organizations. At any echelon, operations on a 10-to-1 basis require standards that become vastly more expensive in first cost and in actual use, because of the type of personnel and time required, than may be warranted by the instruments being tested.