Building-up the DC voltage scale for sources and meters

Previous work has shown that an automated build-up method, called the Reference Step Method (RSM), can measure the gain ratios of a dc voltage source with an uncertainty of 0.2 μV/V up to 1000 V. We have extended this method to also establish the gain ratio of the digital voltmeter (DVM) used in the build-up method. This only requires a few additional measurements so that the gain ratios of the source and meter can be measured simultaneously. Initial measurements suggest that comparable uncertainties can also be achieved for the DVM.