We have carried out a direct comparison between the BIPM and the BNM/LCIE Josephson junction arrays driving them with a single microwave source. The mean difference observed at the 1,018 V level is, 1,2 parts in 10(10) with a total uncertainty. below 1,7 parts in 10(10). By removing uncertainties due to frequency instability, the technique allows closer examination of the other limiting factors in these measurements. In this case we studied the resolution of different detectors.