Cel/F conversion

[brianpos]

I know its noted as a todo, but I also note that the data isn't in the ucum-essence.xml file for it to actually be able to try and do the work. Where did this source file come from. (and Farenheit isn't in the file either - actually it is degF)

[mharthoorn]

We left this conversion out because it is unreliable. Because Fahrenheid and Celcius have both a multiplication and an offset, you have to know whether the temperature is relative or absolute to make a proper conversion.

If the temperature is raised by 100degC gives a different answer than if the absolute temperature is 100decC.

The UCUM spec defines the Fahrenheit to Celcius conversion as one to be a non-default-hard-coded.