It’s said the man with one watch knows what time it is. The man with two watches is never quite sure.
I have the the same problem today, but with temperature.
I’m measuring the temperature of the oven with the oven light on. I’m working on starting a sourdough starter.
Of course the difference that’s being read is on on the order of a few µV. It’s within the margin of error in this case. The type K thermocouple is really optimized for a much higher temperature.
So later on I’ll be making some sourdough of course and that’s a whole other thing. :-)