Lol. You got me curious Secu, as to what you French had before metric took over your lives. What I discovered I suspect answers an awful lot - why you changed, and why we struggled to!
Before the French Revolution, it was thought France had seven or eight hundred different names for various units of measurement, and these measurements varied from trade to trade and town to town! For example, one lieue (league) was 3.268km in Beauce, whereas in Provence it was 5.849km! It's a little known fact that the French Revolution actually began on the banks of the Allier, where the Provencal team took such a mighty offence at the 30th consecutive win by the Beauce team, that a scuffle broke out over the fact the Beauce finishing line was actually several kilometers up stream from the Provence line!
However, on the other side of what the British like to call "The English Channel" - ie the channel of water that belongs to England, and the French like to call "La Manche" - ie the Sleeve (that's the romantic brain for you) the <cough> mighty <cough> British empire had told its subjects via the scribble that is Magna Carta, that "there shall be one unit of measure throughout the realm", and the British plebs, doing as they always tend to do, rolled over on their backs and said to their betters (lords, dukes, landlords, anyone who could spell) 'okey dokey'. So we were quite happy with our one simple system, in comparison to the nightmare of units happening on the other side of The Sleeve.
And all was well with the world until the French removed their pied du roi from their derriere (and their measuring system to boot) and foisted the metric system not only upon themselves, but most of the old Holy Roman Empire, which was happily crumbling away and calling itself Austria and Germany once the subsidence subsided. The trickle down effect reached the British Isles some 160-odd years later and we were finally forced to add some millimeters to the opposite side of our inch-marked school rulers (no sense wasting empty space eh?) and adding some tiny alternative numbers under the mph measurements on our car speedometers which we use to give us a grin when driving on the continent 'doing a ton' when really we're only doing 62.1371 mph. "Look kids - daddy's doing a ton!"
I do need to point out that the ton mentioned above is the old colloquial 'ton', vaguely related to 'tun' - a big measurement of beer, rather than the metric tonne. Beer wins every time - it's the universal constant