The kitchen oven and freezer would be more convenient than water. There is also the question of reducing the excursions with time as shown in a Fluke paper about the 7001 in the reference teardown thread. If you have hysteresis, you need to do that. Consider demagnetization.
Once the curve flattens out, it becomes difficult to determine the deviation from a straight line. The computation becomes very sensitive to numerical precision.
A physical model for the drift and the hysteresis would be very useful. Variations due to stress imply piezoelectric effects so far as I can see. Is there literature on that in solder joints for example?
A man was walking down the street when he saw another man run out, stomp his foot and then go back to leaning against a building. As he approached, the man did this several times. When he reached the man, curiousity got the better of him.
"What are you doing?"
"Keeping away tigers."
"But there are no tigers around here."
"Works very well, doesn't it?"