Linear in this case means y = m * x. The relationship between Fahrenheit and Celsius is affine (y = m * x + b)
For gory details: https://en.wikipedia.org/wiki/Affine_transformation
For gory details: https://en.wikipedia.org/wiki/Affine_transformation
To say it in more detail: To transform between Celsius and Kelvin, you just translate. (That operation is supported in Dimensional.)
To transform between Fahrenheit and Celsius or Fahrenheit and Kelvin, you translate and scale.
We know that Dimensional can scale, because it supports things like miles to kilometers. We know it can translate, because it supports Celsius to Fahrenheit. Is it the combination of scaling and transforming that makes Fahrenheit impossible?
f = m*c + b, which is both a scale and a transform.
f = m*c + b
where m is simply equal to 1. Why wouldn't Fahrenheit conversion be the same thing, just with different constants?
Yeah, you're correct.