Standard reference materials: preparation and use of superconductive fixed point devices, SRM 767

The preparation, testing, and use of SRM 767 devices are described. These devices incorporate samples of lead, indium, aluminum, zinc, and cadmium within a mutual inductance coil pair. These elements become superconductive at temperatures near 7.2 K, 3.4 K, 1.2 K, 0.85 K and 0.5 K, respectively, and the transition midpoints, when attained by observing the sample magnetic susceptibilities in negligible small magnetic fields, provide thermometric reference points which are reproducible to plus or minus 1 mK.