Added two more temp sensors just now! (Well, it took 3 hours, I had to modify the distribution board to add more terminals and stuff.)
One is a probe into the water tank. Currently reading -0.062 C. Which is very interesting, because that water is still liquid. Supercooled? Need to move the probe to not be on the bottom of the upper tank to get a more accurate reading, there could be ice between the tanks. I had some ice crystals in a jug of tea down in the cold well the other day, very refreshing.
The other probe is kind of a spare, I have it down near the bottom of the cold well right now. 0.187 C, and half an hour ago I noticed it read exactly 0.0 C.
Looking forward to some interesting graphs...