The Helsinki temperature scale, used earlier in measurements of the heat capacity of liquid 3He (1-10 mK), is compared with the National Bureau of Standards (NBS) noise and nuclear orientation temperature scale. The superfluid transition temperature (Tc) of 3He at zero pressure and the superconductive transition temperatures of tungsten and beryllium were used as fixed points. Tc on the NBS scale was found to be 1.025 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support the Helsinki data on the heat capacity of 3He.
Lhota, E., Manninen, M. T., Pekola, J. P., Soinne, A. T., & Soulen, R. J. (1981). Comparison of the National Bureau of Standards and the Helsinki temperature scales and its effect on the heat capacity of liquid 3He below 10 mK. Physical Review Letters, 47(8), 590-592. https://doi.org/10.1103/PhysRevLett.47.590