If you give the inch, they'll take the mile.
When I last lived in the UK, it seemed the old systems of measurement were still used for:
-- fevers in F degrees (but weather in C degrees)
-- beer in pints
-- car speed in mph, highway distances in miles and yards
The important stuff changes last, it would seem.
I remember having a very confusing conversation with a supermarket butcher when I asked him for a pound of ground beef. He wanted to know if that was money or weight, and when I said weight, made me do the translation, because his scale wouldn't do it.

In the local butcher shop, though, they didn't have to ask any questions.