Maintenance of a Laboratory Unit of Voltage

Many of the problems involved in maintaining a laboratory reference group of standard cells with a reliability better than one part per million are outlined and solutions suggested. Methods are presented for reducing the number of measurements by approximately 40 percent from the ideal without seriously reducing the accuracy achieved, and procedures for assessing the quality of the group are indicated. Suggestions are given for preferred methods to be used for groups of 4, 8, or 12 cells, and as an example of these procedures the 20-month history of a new group of standard cells is illustrated.