Letter variables? Luxury! One of the calculator had ops like STO, RCL, PAU, GTO, GSB and some numbered "cells", where you could store the result of the calculation.

The other had ops like '74' which were coordinates of the key which activated the given function.

Getting the full screen of the ZX Spectrum surely spoiled me :)

Yeah, that's why math doesn't have self-documenting theorems, right?

Does maths have self-documenting theorems? O.o

Geometrical proofs could be construed as such, even with some propositional logic given that someone comes up with a solid, universal way of expressing it (cf. The Golden Record)

I’d probably have a parallel file with comments.