A Simple Build-Up Method for the DC Voltage Scale of a Source

We report on the performance of a simple method, known as the reference step method, to build up the dc voltage scale of a source. The key advantages of this method are that it relies on equipment that is readily available in most high-level laboratories and can be fully automated. The Type A uncertainties achieved by this approach can be less than 0.1 <formula formulatype="inline"><tex Notation="TeX">$\mu{\rm V/V}$</tex></formula>. This performance is achieved because of the excellent differential linearity of the DVM used in the method. We have validated the overall accuracy of the method by directly comparing this approach with more traditional resistive divider techniques and have established that the expanded uncertainty is better than 0.2 <formula formulatype="inline"><tex Notation="TeX"> $\mu{\rm V/V}$</tex></formula> up to 1000 V, limited only by the performance of the instruments used.