The weird thing is that it filters through to wheels too. So you get "700C wheels", which are really just 622 mm rim.
Which - as I understand it - is "the diameter of the rim that would be needed to be paired with a non existent obsolete tyre of size "C" to get an overall diameter of 700mm."
That knocks your feet and inches, rods poles and perches and other obsolete units into a cocked hat.