Recent Progress of the 2e/h Measurement at PTB

In this paper, an experimental setup is described with which the stability of the PTB voltage standard, consisting of a group of International Weston cells, can be monitored with a total uncertainty (1σ) of 4 parts in 108 by means of the ac Josephson effect. The measured quotient of the fundamental constants 2e/h is given by 2e/h = (483 593.606 ± 0.020) GHZ/VPTB, May 1972.