In reply to GridNorth:
Sustained difficulty numeral... gottit
Protection numeral... gottit
Rock quality numberal... gottit
> Fourth numeral: denotes predominating holds and moves associated with them.
Don't get this one. It seems to duplicate the technical grade, which would partly be based on these? Also, it sounds best suited to steep limestone but don't think it would work so well on other mediums/angulations. Where would easy, smooth granite slabs fit into the equation for example?
Worth pointing out that the Rockfax guides have the symbols for the first three numerals, although obviously not scaled. They do help to explain deviations between overall and technical grades without the waffle though.