As someone who has long considered himself a “pure math” person, as opposed to more of a “science” person, I never really cared much about the units of expressions; kilograms, meters, Newtons, and the like. The numbers were all I ever really cared about. Well now I see what can happen when this attitude is taken too far.
It took me about 3 days of driving around Puerto Rico before I realized that speed limits were posted in miles per hour and mile markers were posted in kilometers. Driving around a foreign country (territory?) is challenging enough without having to perform a bunch of conversions in your head.
Just to further complicate matters, plenty of signs left it open to driver interpretation.