It's not like that. Fahrenheit is not based on the freezing and boiling point of water, which is used32ºF and 180ºF as a reference, if not, it would result absurdo. No it serves to consider it the same claiming that water freezes at 32ºF because it is known. It does not make it reconstructible, essential in science. You can't work with randomly obtained values if you use a fixed reference like water, how do you want to determine a zero point without do all kinds of conversions in physical or chemical applications and experiments? Sure, you can put a thermometer on ice and in boiling water and then put a scale between 32º and 180º instead of between 0º and 100º, to measure in Fahrenheit, but this does not solve the problem of reconstructibility of these units. Fahrenheit set the 0ºF and the 100ºF on the scale by recording the lowest temperatures he could measure and his own body temperature, by being in a slight state of fever. He took the lowest temperature that was measured in the harsh winter of 1708 to 1709 in his city of Gdansk (Poland), about -17.8 C, as point 0 F, with this we have the same problem as with the other imperial units, they lacks an exact unit for the reconstruction, not better than the pie as unit for the lenght. Even the Réaumur scale is better, also use 0º for the freeze point of water, but using a octagesimal scale where water boils at 80º instead of 100º in C.