I have tested again running for over 24 hours and I get s similar result.
Here is the test rig now:
This is the results:
I'll attach the data.
If anyone else tests these and gets a different result let me know.
Note low res ADC on nano. 128 microstepping on motor/rail setup from an old up mini i think it was.
10 seconds between samples.
edit.. 60,000 char limit.
Edit: Despite starting at room temp 23.75C, heating up and cooling down , and remaining at 23.75C for some hours the probe still triggers at some 10um different that when the testing started 23h earlier.