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xkcd #3001: Temperature Scales
(xkcd.com)
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I once read that circular thermometers were a thing and that's why fahrenheit has 180° between freezing and boiling.
I think a degree F was 1/10,000 of the volume of mercury he happened to use in his first thermometer. The 180 was probably a coincidence because bimetal spring thermometers came along later.
I've heard this too. It also allows for easily making your own thermometer, since you can just divide by 2 until you get all the way down to degrees.