Present Estimates of the Differences Between Thermodynamic Temperatures and the ITS-90

At the request of the Consultative Committee for Thermometry (CCT), Working Group 4 (WG4) has critically reviewed all available measurements of the differences between thermodynamic and ITS-90 temperatures, (T - T (90)), and documented the conversion of older data to the ITS-90. Particular attention has been given to the uncertainties. Based on this review, we provide consensus estimates of T - T (90) for selected measurements from 0.65 K to 1358 K. We provide two analytic functions for T - T (90), one for use from 8 K to the triple point of water (T (TPW)) and one for use above T (TPW). The small discontinuity of the derivative dT (90)/d T at T (TPW) is discussed. We also identify temperature ranges where researchers are encouraged to undertake high-accuracy measurements of T - T (90).