I am starting to get back into color processing (C41 and E6) and I need a really reliable thermometer for this. I have a $4 glass thermometer that I bought at Freestyle which yields my body temperature to within a degree C and that's been good enough for my black and white work. I also have a fancier Premier Large Dial thermometer, but it disagrees with the glass thermometer by a degree or two (C or F I can't remember). Any way, these thermometers are both a little difficult to calibrate since their range does not cover the ice or boiling water temperatures (standard lab calibrators).
My question: Can anyone recommend a reliable thermometer for color work which I can use for color and to better understand my existing thermometers and derive corrections for them. I don't care if it's metal or glass. There is one being sold by Patterson called the "12-Inch Color Thermometer", priced from about $25-30. I was thinking of this one, but I'd love to hear other users experiences. I know Patterson is a pretty serious company that usually makes good equipment. I have one other related question: does anyone use "aquarium heaters" to warm C41 chemicals. I have an Arista C41 kit that wants the developer held at 102 F, so elevating the temperature of a water heat bath in contact with the various chemical tanks in a thermostatically controlled way seems to be a good approach.