@MililaniVF (2/3) However, I had learned how to approximate square roots, and the upper bound on the approximation error, using calculus. I had paper and pencil, so I calculated our diagonals to the precision I felt we could measure. I wonder if my mother made me calculate the diagonals (instead of doing it herself) to make her point that I should remember it too. I suspect that my solving it (thereby ruining her lesson) with calculus (the only math she dreaded) probably pissed her off royally.