Longboard Surfboard

A long board is usually 9' or longer with a rounded nose and square or round tail. It used to be that a rope was strung across the beach between two palm trees and if the surfboard was touching the sand and the rope then the surfboard was long enough.  Occasionally, a shorter lady would pull out the old school rule book which state the surfboard need only be 3 feet taller than the surfer.  Who's rule book?  Please share if you know!