Hi,
Just for the fun....
1e, 10V reference in a oven, measured with a fresh calibrated 3458a (+0,45PPM)
HP 34401A, 10V range 100PLC.
Keysight 34461A 10V range 100PLC.
Keysight 34461A 5K thermistor measuring the Temp in my LAB.
The measured time is approximately 24 hours.
The Temp measurement...
10V 34461A after the use of zero key.
The 34401A and 34461A are both very good, they are less than 1PPM / Celsius :-)
Kind regarts,
Bklackdog