A program to upgrade the accuracy at which the volt is maintained in an industry standards laboratory using four solid state reference standards is described. The upgrade involved first characterizing the four references using a Josephson Array Voltage Standard over an period of several months, and then carrying out two Voltage Measurement Assurance Programs at the user laboratory at six month intervals. After the completion of all of these measurements, it was possible to predict the bank average of the solid state standards with an uncertainty of less than 0.5 parts in 10~(6) over a one year period with a coverage factor of k=2.
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