Its a bit difficult to remain imperialistic when we lost our empire around about 1945!
I gather, and I am not at all surprised, the WWII GIs had enormous problems with our old currency of £sd (pounds, shillings and pence);- 12 pennies to a shilling, twenty shillings to the pound, 240 pennies to a pound. A half crown coin was worth two shillings and sixpence, a florin - two shillings. Then we had the ten-bob note, the tanner, the thrupenny bit, the ha'penny, the farthing and much much more!!! (As a boy I remember a half crown as being a decent sum and a very nice coin, real money!.)
In 1970, to show our genuine lack of imperialism, we gave in to your demands and decimalised our currency but what that has to do with diving I am not sure.
At risk of repeating a point that may have been made in an earlier post. "Metric" refers only to the measurement of length using metres. "Imperial" refers to length, volume, weight, pressure, density, viscosity etc, etc.
At school I was taught in SI units (Systeme Internationale?) which is a decimal system, including metres, litres, grams, pascals etc. Trouble was most retailers continued to use the imperial system of weights until it became illegal, yes illegal, to sell fruit and veg. in lbs.
An atmosphere is 1 kilpopascal.
As for house building, Groundhog, when we first went metric wood was still sold in feet but this was known as a "unit" length in the trade for quite some time. I am just about to start construction of a new surgery/pharmacy and all the measurments are standardised in metres, which fits in with the raw materials, which are now (thankfully) sold in metric units. Plywood? 2 x 3 metres, I think.
As for diving
Although we now use metres of sea water for depth all standard Buhlmann deco tables are based on 10,20, 30. . . foot stops. For the BSAC '88 tables we have simply rounded these figures up (or down) to the nearest whole-number metric fit :- 3,6 and 9 metres and an ascent of 30 ft/sec is rounded up to 10 M/sec (the actual equivalent is 32.5 ft/sec)
SAC is so easy to calculate using bar for pressure, cylinder size;- its water capacity in litres and SAC in l/min. Mine is 17 l/min so at 10 mtres it is 34 l/min. My twin 10s at 232 bar contain 4,640 litrs when full which gives a rock-bottom figure of 4,640/34 = 136 mins.
If I want a 50 bar reserve I have enough air for
20 x (232-50) = 107 mins
34
That took about 30 seconds. How long does it take to calculate it in imperial units?
By the way, we still buy milk and beer in pints!
We buy petrol in litres but still measure fule ecomony in miles per gallon, distance in miles and speed mph.(and we drive on the left to leave our right hand free to fend off approcahing highwaymen with our swords!)
and epinephelus, the artillery here do not use degrees they use mils, but you've guessed it, there are more than 1000 mils in a circle (I can't remember the figure off hand and I have never been told why. Probably a mil was the limit of resolution for artillery accuracy.)
AND, yes, we all still tell the time in seconds, minutes, hours, weeks, months and years! (hardly a decimal system.)
Confusing, isn't it!
and by the way. I am not a Euopean! They are very odd people across the sea who talk funny and do not have a reigning monarch even if she no longer has an empire!

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