You've just reminded me, Graham, of the multitude of minor roads in Oz named
"One Chain Rd". And, while I have always known the length of a cricket pitch as "22 yards" (or even "1 chain") and the dimensions of a netball court as 100'x50', with 10' high goalposts, my daughters have to quote them in metres when passing their umpire theory tests. And the nearest an opponent could defend without inviting the "Obstruction" infringement was always 3'; now it's 0.9m and a bit more variably interpreted, 'coz nobody can find a 0.9 folding carpenter's rule to keep in their umpiring clobber

Cheers, Rowan