Eric
Different numbers are different lengths, I get a number 4 back & sides and usually a 5 or 6 on top. ehow.co.uk/facts_5... Are these things not used world wide?
Martijn
I have never, ever, heard about that! Not back in the Netherlands nor here in Sweden. Don't recall having seen it in Germany either, though full disclosure, I have never had my haircut whilst in that country.
🦿 Lucian Marin
It's used here, but mostly for men. Two weeks ago a got a hair cut with the number 3 on back and sides and scissors on top. It's possible that women hair salons don't use hair clippers.