Zimbabwe (Rhodesia as it was then) went metric in 1970. We were using the old imperial system up to then; acres, pounds, ounces, miles, feet and inches etc. The property my mother owned in Penhalonga was measured in morgen. The metric system is far easier to use. Like I mentioned to my sister in the USA it’s all in base 10 and length and mass are related. Want to convert metres to kilometres? Move the decimal point! Despite all this, 45 years later, relics of the old system remain.
Yesterday in the industrial sites of Harare I was shopping for hardware essential in our annual maintenance programme. I blithely asked for 25kg of 6 inch nails! I could have asked for 150mm nails and everyone would have known what I was asking for but try saying “150mm” and then “6 inch”. Much easier to say 6 inch! Relics exist elsewhere too, nowhere more bizarrely than in plumbing. Old style copper and steel piping is measured in inches and refers to the internal diameter. PVC piping is measured in mm and refers to the outside diameter. It is a blatant conversion of the old system; 50mm is 2 inches, 32mm is 1¼ inches etc. Speed and distance are all firmly metric as is temperature and mass. ºF is utterly meaningless to me though I can grasp pounds weight and speed if I think about it. That the weight of the recent UK royal baby was measured in pounds didn’t mean much except that I think it was in the normal range.
One day the world will actually share the same system of units and we will look back at the old system with puzzlement and wonder why we put up with it for so long. That it costs the USA (and presumably Liberia and Burma) vast amounts of money to not metricate is beyond doubt. The only disputed fact is how much.
For a fascinating and entertaining read on the invention of the metric system (amongst other things) read Chet Raymo’s “Walking Zero”
Zimbabwe Absurdity 
I learned many years ago from some Australians while traveling in the U.K. that one “doubles and adds 30” to convert centigrade to Fahrenheit, the measurement we use for temperature in the States. I hear people say 30 is hot and shiver and sweat at the same time. But doubled, plus thirty, and 90 sounds hot indeed to me! I have similar issues in reverse as an American in Zimbabwe. 🙂
Another relic is wheel sizes, both bicycle and automotive. The “10-speeds” of our youth were all 27 inch, which were replaced by the metric 700 C. It’s quite hard to get 27 in. tyres these days for “veteran” 27 in. 10-speeds. But mountain bikes are still quoted imperial, 26 in. was standard, but is being rapidly being overtaken by 29 in. “29 ers”, plus the intermediate 27.5 in. All imperial and must really irk the French, though sadly they seem to have ceased being the big manufacturer of bicycles they were during my youth! Not surprising though, and the mountain biking boom was a US led thing.
Car rim and tyre sizes as well. The 14 in. seemed to be OK even for the Lamboghini Countach, but nowadays you need the bling 22 in. wheel size to score. All still imperial, and the metric nations making Michelin, Pirelli etc have to fall in!
I did write some years ago to that bastion of publishing and mixed units, National Geographic magazine asking them their policy on units in their articles. I also suggested an article on just that; units and their use and origin worldwide. They didn’t reply or publish the letter and haven’t done the article!