[rob74]

> Several accounts of how he originally defined his scale exist, but the original paper suggests the lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from a mixture of water, ice, and ammonium chloride (a salt). The other limit established was his best estimate of the average human body temperature, originally set at 90 °F, then 96 °F (about 2.6 °F less than the modern value due to a later redefinition of the scale).

Nothing beats scientific accuracy and thoroughness, right? So it then actually ended up being tied to water as well:

> For much of the 20th century, the Fahrenheit scale was defined by two fixed points with a 180 °F separation: the temperature at which pure water freezes was defined as 32 °F and the boiling point of water was defined to be 212 °F

(from https://en.wikipedia.org/wiki/Fahrenheit)

[Leftium]

So that's why one unit Celcius is roughly 2 units Fahrenheit!

For some reason I never noticed there are exactly 180 degrees between freezing and boiling points on the Fahrenheit scale. 100°C is a nice "round" number, and 180°F divides evenly into a lot of smaller numbers.