Each day the English drive miles defined in metres and drink pints of beer defined in millilitres, while in the USA, people watch football where the main scoring is done over an exact distance of exactly 9.144 metres.
Also the Welsh, Scottish and Northern Irish drive in miles. That's because England is part of a United Kingdom - rather than the name of this (group of) Islands. Granted - the roads in Welsh are labelled milltir and llath (miles, yards) as well as the English version
It¹s called hidden metric¹.
I'm not convinced that a=b makes 'b' a hidden version of 'a'. I see where you're coming from but you can apply the argument both ways.
Also I'm pretty convinced that the average Brit driving up the M1 is going to see hidden metric in the miles and yards he or she sees.
A lot of jam pots here are sold as 454g. I would see that as 454 metric grammes rather than 'hidden imperial' - even though the argument is more compelling here due to the round'ness of "one".
