An Alcohol thermometer is a useful piece of equipment. Has to be Alcohol, as they only freeze way below -100C. -160 c or something?
I used to carry one of those round, plastic bodied ones we in Scandihooligania fix on the outside of the kitchen window, but I am not sure if you can find a good one in UK.
Those glass bodied long ones are better of course, but need to be protected well or they break.
Once at home, you can place it in your freezer so you know the 'real' temperature.
The thermometers supplied with the freezers I am not so sure about, the ones I own all show different temperature.
(I will not make those "Arctic threads" as it is better you ask specific question, I think. I do not want to bore you needlessly!
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