This is a special post for quick takes by jsd. Only they can create top-level comments. Comments here also appear on the Quick Takes page and All Posts page.
If you're trying to explain why we see straight lines on graphs when plotting Y against X, your explanation shouldn't also predict straight lines of graphs when plotting f(Y) against X for any function f.
...why not? Being serious here, straight lines should at least work in the short term unless the second derivative is big, which is the claim, and for other things we opportunistically choose f(X) and a g(Y) to make it straighter.