If I have a set of stage distances for the decade, for example
100 km, 200km, 150km, 120 km, 175 km
I sort them as follows:
1. 100 km
2. 120 km
3. 150 km
4. 175 km
5. 200 km
But each decade has a different number of climbs, so I normalize the rank to fall between zero and one, as follows:
0.1, 100 km
0.3, 120 km
0.5, 150 km
0.7, 175 km
0.9, 200 km
You can see here each climb falls within a bin which is 1/5 wide.
But obviously the difference, statistically, between 0.001 and 0.011 is a lot bigger than the difference between 0.500 and 0.510, even though both differ by 0.01. So then I do the logarthimic transformation ln | r / (1 - r ) |. On the above numbers, this becomes:
-2.2, 100 km
-0.8, 120 km
0, 150 km
0.8, 175 km
2.2, 200 km
Basically it's just a scheme to represent graphically the distribution of climb lengths for decades with differing numbers of climbs, sort of like a histogram but with better detail.