With a temp. rating 0-50 C, 1ppm/C 22V input from regulated bench supply to an IET High Stability Voltage Reference module, or HSVR-6.3, specified at 6.2998V (ref. NIST). At first power-on it read 6.299995V then started settling down. Measurements made with in-factory-calibration Keysight 34770A, auto-caled @ 18.5 C (stable) and set to 1G input. HSVR has been sitting in its original packing and box for over a decade, never powered up until today. P.S. Sorry if procedural errors in posting and forgive me, I'm just now learning about the statistical end of this hobby. George Dowell (Geo) PICTURES LINK: http://www.qsl.net/k/k0ff/VOLT_NUTS/IET_HSVR_6.3-FIRST%20_LIGHT/