Experiments utilizing the ac Josephson effect already provide a precise means of monitoring the stability of some of the nationally maintained standards of voltage. The advantages to be gained from operating most components of such a system at cryogenic temperatures are described. Possible measuring systems are outlined and progress made towards their realization is reported. This includes the development of a transformer-matched Josephson double-junction galvanometer, mechanical superconducting switches and cryogenic resistors with a very low temperature coefficient of resistance. (Author)
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