Originally Posted By: jpeck
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they do not need to be “calibrated” to the ice water if checking TD, but “calibrated” to each other (because you are checking difference, not actual temperature).
Insert your thermometers, wait for them to stabilize, take the readings, swap thermometer positions, wait for them to stabilize again and read them again.
They should be reading within 1 degree of each other regardless of which thermometer is where.
To calibrate with glass filled with ice, fill a glass with ice, pack in as much ice as you can, add enough water to fill the the glass to the top of the ice, repack the ice and add more if you can. Insert both thermometers and adjust to 32-33 degrees. That is about as close as those thermometers will read anyway