[Coda]

Originally Posted by Quiet Man Cometh

Celsius decided to set 0 degrees at water's freezing point so yeah, it's cold.

I think Fahrenheit set 0 degrees at the coldest measurable temperature at the time. Thus it seems a little arbitrary now, but made sense back then.

It would be nice if the degrees were the same size though. Not sure how they decided what the difference between degrees would be on either side.

In both cases, the size of the degree is determined by TWO set points on the scale.

Fahrenheit used a cold winter day for his 0 point and his own body temperature for his 100 point. Apparently, it was a VERY cold winter day, and he was sick at the time. Once he had marked off the scale on his thermometer, he could calibrate new thermometers against the old ones without having to find exactly the same original sources.

Celsius saw the problem with having unrepeatable calibration and chose to set the 0 and 100 points based on something you can easily reproduce: the temperature of water as it's freezing (because it won't go past 0C until it's frozen), and the temperature of water as it's boiling (because it won't go past 100C until it's vapor).