🔧 A formula can be implemented perfectly and still give the wrong answer

I spent a while this year writing a small zero-dependency library of health and fitness formulas — BMI, Mifflin-St Jeor, the US Navy body-fat equation, FFMI, Epley and Brzycki, Karvonen. Thirty-odd functions, no dependencies, ESM, one file.

It should have been a boring job. It mostly was. But three things came out of it that I think generalise...