Despite the fact my schooling was done with the metric system, have had to become reasonably familiar with imperial -- dealing with "old people" (ducks a flying spanner). Then theres the fact that a fair bit of the caravan stuff I deal with is still in feet. So I ensure all the tape measures in the shop have both measurements on them.

Base 10 number system --- dunno how difficult that can be!!

Bought a block in town about 15 years ago -- damn thing was still measured in links (subset of chains apparently). Even my solicitor (well into his 60s back then) had to pull out the conversion tables for that one.