Freezing point of pure water - but saltwater/brine freezes as a different temperature.
pure water at mean atmosphere pressure at sea level if we’re getting technical, but frankly human body temperature varies from 35.5C (95.9F) to 37.5C (99.5F) anyway, and that’s before considering when people are ill, so if we go down that route it falls apart quickly enough that the definition of 100 given above is clearly just as arbitrary
I’m okay with “mean atmosphere pressure” bc that’s what is most likely to occur, whereas pure water seems far less likely to be found in a coastal village. The oddness of the measuring abilities of the devices made at the time is a more damning argument, but less for them back then and more for us now. Still, roughly negative ten to 40 for Celsius vs. roughly zero to one hundred for Fahrenheit, the latter does seem to use more “natural” numbers, even if nothing else about non-metric systems makes any sense.
