Recently there was some disussion here in pow-teach about which measurement units should be employed in our problems -- metric or U.S. customary. It caused me to reflect on things here in the country where I live, El Salvador.
When we buy gasoline for our cars, we purchase in 'gallons'; yet we leave the station and drive to the next town in 'kilometers'.
When my wife buys "un litro de leche" [a liter of milk], it's really a quart of milk, but only printed on the carton as "946 ml". [No, it doesn't give it in "cuartos", but in metric terms.]
When you ask someone how tall he/she is, they might answer in one of two ways: (1) ciento sesenta [one hundred sixty], the assummed unit being centimeters, or (2) uno, sesenta [one, sixty], assuming "meters, centimeters" (much as one assumes the phrase in the "States" of "five, nine" to mean "5 feet, 9 inches".
There are a few other oddities, but this gives the idea that one must be flexible and capable in both systems still.