Being a non-native English speaker and having monaural hearing¹, the first time visiting the USA I thought they mentioned Empirical Units² when they tried to explain miles, feet and other measurement units they use on their island.
Then I learned they are in fact United States customary units but in the USA, they actually name those Imperial Units, implying that the UK still has a very strong influence on the USA. In reality, there are differences³ between Imperial Units and United States customary units to keep things in the USA practical (or lazy if you want), so I will keep calling their system Empirical Units as it is more fit for purpose (can’t name them Freedom Units any more given their Project 2025 regime).
Anyway, quite a while ago there was this cool XKCD “The Maritime Approximation” (image on the right) including only Imperial Units holding for Empirical Units as well: π mph ≈ 𝑒 kn (let’s use ISO unit symbols here, shall we) which is correct to < 0.5%.
Recently, I learned that with the same accuracy, there is a golden ratio between metric and Imperial/Empirical Units: 𝜙 km = 1 mi, also correct to < 0.5%.
Kevlin Henney wrote two great blog posts on these explaining way more background information:
