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The reproducibility of the IPTS-68 as determined by forty-eight thermometers is shown to be within approximately plus or minus 3mK in the range 13.81 K to 20.28 K, plus or minus 1 mK in the range 2.28 K to 54.361 K, and plus or minus 2 mK in the range 54.361 K to 90.188 K. In the range 90.188 K to 273.15 K, nine thermometers exhibit a scale reproducibility within only plus or minus 5 mK; it is believed that this figure is limited by calibration uncertainties, and that plus or minus 1 mK is more likely to be typical. (Author)

In the region 13.81K to 90.188K the IPTS-68 will replace a number of previously used low temperature scales, four of which are NBS-55, NPL-61, PRMI-54, and PSU-54. It is desirable to know the relationships between these scales and the IPTS-68. At the present time these relationships can be determined, though indirectly and somewhat inaccurately, by means of an earlier intercomparison of the scales, their relationships to the CCT-64 table, and estimates of the values of the defining fixed point temperatures of the IPTS-68 on this table. Values of these relationships are presented. (Author), Prepared in cooperation with Leiden Ryksuniversiteit (Netherlands). Kamerlingh Annes Lab. and National Physics Lab., Teddington (England).

A description is given of the scale of total irradiance maintained at the National Research Council. This scale, in contrast with other national scales, is derived from a low temperature (50 to 150C) blackbody, rather than from a high temperature (over 1000C) blackbody or an absolute radiometer. The irradiance from three tungsten-filament lamps has been measured on this scale as part of an international programme to intercompare irradiance scales. The results of several tests for systematic errors in these measurements are discussed. (Author)