gh-temperature secondary standards Range to 661°C Meets all ITS-90 requirements for resistance ratios Rtp drift &lt, 20 mK after 500 hours at 661°C Calibrated accuracy of ± 0.006 °C at 0 °C Fluke Calibrations high-temp secondary standards fill the gap between affordable, but temperature-limited secondary PRTs (platinum resistance thermometers) and more expensive, highly accurate SPRTs (standard platinum resistance thermometers).