I'm a mile man when it comes to distances. But like Gasket and Don, I grew up in school that worked the metric system into our math education. Since my 1 foot long school spec'd ruler had inches on one side and a 30+ cm/mm side made things super easy plus any dummy should be able to count to 10 and multiply and divide by 10. Also, how hard is it REALLY? Our money is based 100's and fractions thereof. From penny to nickel to a dime to a quarter to a dollar etc. A penny is 1/100th of a dollar, therefore 100 pennies = 1 dollar. A cm is in a similar proportion as a penny is to a dollar. A cm is 1/100th of a Metre, now just interchange a penny for a cm and a dollar for a metre and you are in business. Unlike the cm/mm relationship, there is no 1/10th of a penny, but all one has to know is 10 mm's = 1 cm and it is simple as that.
Kind of like DonP says, we learned without even thinking about it...
As a carpenter, I am fully capable of measuring quickly in Inches, fractions of inches, mm's cm's, yards( length NOT cubic yards of volume), Metres, KM's if needed etc. Heck, many times I used the manner of measuring I like best, " the dummy method"
This is where I take an item and put a mark on it and whatever that measurement is is irrelevant because it is THE measurement. I make my cut there.
Heck there have been times I have even taken my pencil and laid it against some place on my work and eyeball where the length falls between 2 letters on the name or specs of the pencil and then lay it on my wood and mark the length between the E and the Z or whatever LOL.
As for pounds, shillings etc, WTF is a quid?
Now back to measuring lengths,,,,,,,, As a carpenter like I said, I can measure in all manner of whatever you call ems. BUT don't give me a tape that is so "busy" with all types of numbers like Harry Homeowner tapes that have 1/16 1/8 3/16 1/4 3/8 etc etc etc etc all printed out so as to make it nearly impossible to read the little lines and the big number 1, 2, 3, 4 INCH, CM etc marks that make quick sight reading of a tape SIMPLE and easy.
Some of our tapes come so full of numbers I can't use em. I do not need tape measure makers to label each 1/16 or 1/8 like the one pictured below because I can count or divide or multiply. Those extra numbers just foul me up if I need to pull a measurement from right to left or left to right. I can't read either side of the tape by instinct because of all those extra fraction numbers in the way.
Same goes for this Metric/Imperial tape. While I can read it in time, it slows me down having to "see" the measurement when the sight picture is "too busy"
Ideally I want a tape with all one scale of numbers, 2 sides of graduations in the same breakup of increments on both sides like these.
I have no clue what Smitty just said....re: shires and tolkiens, but I fully understand esgee speak.
I remember doing metric somewhere around 1972-74 at about 8-10 years old. Little did I know I would be using a tape measure every day of my adult life after age 24.