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 d T 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 .