Question: what does 1 in 20 gradient mean?
Answer: For the parts of an accessible route that aren't a ramp, the maximum running slope allowed is 1:20. That means for every inch of height change there must be at least 20 inches of route run. The distance from the bottom edge of the level to the surface should be no more than 1.2 inches (1.2:24 = 1:20).