Abstract
In most key and regional comparisons of Josephson voltage standards (JVS) the Type A uncertainty is assumed to be the standard deviation of the mean of the measurand calculated as if repeated measurement values were uncorrelated. In a recent JVS key comparison (BIPM.EM-K10.b) between the Bureau International des Poids et Mesures (BIPM) and the National Institute of Standards and Technology (NIST), an alternative protocol was used by the NIST to enable automatic data acquisition over 14 hours. After correcting the data for residual dependence on barometric pressure, the 218 individual results are sufficient to numerically characterize autocorrelation effects. The analysis shows that the Type A uncertainty is limited by 1/ f noise in the DVM used as the null detector.
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