10 days a week? Why. Because we have ten fingers, oc. 13 months was a year in the matriarchy, the lunar months... 12 was the monarchy and the church. We are back to 12 bc it is divisible for more numbers. But the metre was the great FR's legacy. It is under a dome, and you pay if you want a copy of fraternity. A inch does not exists. It's a just a fraction of the Paris' metre.