 The original intention was that the classes would be subdivided decimally, so that a route graded 4.5 would be a scramble halfway between 4 and 5, and 5.9 would be the hardest rock climb.Increased standards and improved equipment meant that climbs graded 5.9 in the 1960s are now only of moderate difficulty.Rather than regrade all climbs each time standards improve, additional grades were added at the top—originally only 5.10, but it soon became apparent that an open-ended system was needed, and further grades of 5.11, 5.12, etc.