Re-evaluation of uncertainty for calibration of 100 MΩ and 1 GΩ resistors at NPL

The uncertainty for calibrating $100$ M$\Omega$ and $1$ G$\Omega$ resistors using the NPL high-resistance CCC bridge has been re-evaluated, resulting in combined uncertainties of $\sim 0.1$ $\mu\Omega/ \Omega$, considerably smaller than the CMC entries of $0.4$ $\mu\Omega/ \Omega$ and $1.6$ $\mu\Omega/ \Omega$ respectively. This re-evaluation supports measurement of single electron pump currents with combined uncertainties of a few parts in $10^7$.