Thing is, you usually define all your variables. At least we do in engineering (of physical variety, rather than software).
Mostly because we can’t expect everyone reading the calculation to know, and that not everyone uses the same symbols.
Not explaining each variable is bad practice, other than for very simple things. (I do expect everyone and their dog reading a process eng calc to know PV=nRT, at a minimum).
Just like (in my opinion) not defining industry specific abbreviations is also bad practice.