Paris point
The Paris point is a unit of length defined as. It is commonly used for shoe sizes in Continental Europe.
The unit was invented by French shoemakers in the early 1800s. Its origin probably lies in centimetre being very close to inch; a French inch Units_of_measurement_in_France_before_the_French_Revolution#Length is around 27 mm, a quarter of that is 6.7 mm, close to 6. mm defined for the Paris point.