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Right idea but overly complicated. Assuming you use fresh water, if you mix a generous amount of ice and water in a bucket and wait a few minutes for the temperature to equalize, the water temp will be exactly 32 degrees and no thermometer will be needed.
Fresh water ice melts at 32 degrees and it takes a great deal of energy for the ice to undergo the phase change to water. Consequently as long as there is ample ice in the water and the two are not allowed to stratify, the temp will be 32 degrees.
So...dump a bag of ice in bucket, add water, wait a few minutes, put your console in and see then track the temperature to see 1. how much lag there is as the thermometer cools (the rate of change will probably get much slower as the temp approaches water temp) and 2. to see what the final temp is and how far it deviates from 32 degrees.
Just a bit of correction. It's at 39F/4C which water have the highest density. Other than that, the rest is very accurate
When ice diving in lakes one will "always" find temps around 39F at the bottom, and colder further up underneath the ice. In our fiords there's an interesting phenomena as the water can be VERY cold on the surface. Perhaps 34-35F. With surface temps like these I've personally experienced 8C/46F at 30m/90ft in the Oslofiord! This is because salt water is even denser, and with no wind cold freshwater from rivers float out on the surface of the fiord like a carpet, not mixing with the warmer sea.
If you don't have to cut a HOLE in the top to get in...
...THE WATER ISN'T COLD!
I have never seen 39 degrees at the bottom of a frozen lake!!! That would be nice!!! Last winter, 14 of us went on one of the usual weekend ice dives. 6 of us had a temp on both computer and analog of 31 degrees. 4 had 28 degrees. 3 had 29-30 and one had 32. Are you going to tell me that only one diver had the correctly callibrated dive gear??? All of the above divers went to different depths and this was their coldest temps. Only "pure" water freezes at 32 degrees. I doubt that any of us have this kind of freshwater in our lakes or streams (minerals, traces of chemicals, fertilizer run offs). The motion of water also affects it's freezing temperature. (Underwater springs, rivers, etc.). Sediment can also effect freezing. So it is actually possible to have an accurate reading of 30 degrees....
Now that I actually think about it, 39 degrees would be nice at the bottom of the lake in the middle of July!!!!
Exactly who the hell do you think you are insulting me like that? I was NOT insulting anyone else on this board. First of all, since you have never dove it and seen it does not mean that it's not possible. Maybe the United States Department of energy would be able to clear this up for you. I'm NOT saying water does not freeze at 32 degrees. I am simply stating that PURE WATER freezes at 32 degrees. Factor in what I stated before and you have a different temperature.
Telling me if I go deep enough? How the hell do you know how deep I've been? HUH??? Maybe you should actually dive and not spend so much time in SCHOOL. The Great Lakes are considered a Freshwater lake. Or don't they teach that in your school??? Water temps in the summer get below 39 degrees at depth depending on location. That fact can be verified by the State of Michigan.
Now where'd I leave that chestnut??? Gotta go diving....