How much harder is one grade?

Inspired by, EpicTV's - The Great Grade Debate here are some further thoughts which goes back to the original article from 2002 - Rating in theory and reality - "Everything is relative" The harder it gets, the harder it takes to progress. To advance in grades from 5c to 6a normally just takes a couple of sessions meanwhile for Adam Ondra it will probably take several years to progress to 9c+. The easiest way to establish how much harder one grade is possibly to use a pyramid-multiplicator model of around 4, based on how many climbers have reached a specific grade. (For boulders the multiplicator is much higher.) 1 = 9c (Adam Ondra) 4 = 9b+ (Ondra & Sharma) 16 = 9b (Some 16 guys) 64 = 9a+ (Some 69 guys) 256 = 9a (Guessing 200+ guys) Another way of explaining how much harder one grade is, is to use the 8a Time Comparison Grading Theory, at least for experienced climbers. The speculated time and effort needed to advance one grade for Adam Ondra with a 9a maximum onsight capacity could be, talking about personal bests; Onsight = 9a Flash = 9a+ 3 Days = 9b 20 days = 9b+ 150 days = 9c For less experienced and relatively less technically and tactically skilled; Onsight = 8a Flash = 8a+ 3 Go = 8b 3 Days = 8b+ 15 Days = 8c 100 Days = 8c+