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It's a "typo", not a technical error. I read, and was confused by the sentence "If you don't want to measure the temperature Trough the serial interface ..." (and judging by the comments, I wasn't the only one). Trough made me think of waterbath, and other experimental techniques.The author intended to say (and has since corrected it to) say "Through", not "Trough". A minor issue in an awesome instructable.
Thanks for the instructable, I intend to use a lot of what you've done. Incase you haven't already thought about it, you should beware of legionaire's bacteria growing the water at temperatures up to 48 degrees. You'd need to periodically get the water to 60-odd degrees to kill off the bacteria that have already grown.