The confusion in the ranking system is because:
- The male and female rankings are written using different notation, and
- The female rankings give the appropriate power levels on two different scales.
Strength in saidar
The initial scale describe in the book is implied to be how the Aes Sedai rated themselves internally. This power ranking system had 60 levels, with 1 being the highest. The strongest channelers (e.g. Moraine) were ranked a 1, down to the weakest, rated a 60. Anyone below that was considered too weak to be accepted as a Novice.
The problem arose when the Two Rivers girls showed up; Elayne, Egwene, and Nynaeve all had strength in saidar that was way past rank 1, and that was before they ran into Windfinders and damane that were even stronger. So, they had to invent a new ranking system, by adding 12 new ranks to the top end, and pushing all the other ranks down. Under this system, Nynaeve is a 3, while Moraine is now a 13.
The Companion lists power rankings for female channels using the notation new system ( old system ), e.g. 1(13). However, for the newly added top-end levels, there is no value in the old system. In this case, the notation is new system ( +levels above old system ).
So, for example, Moraine is at level 1 in the old system, which becomes level 13 in the new system, so she is a 13(1). However, Elayne is a level 8 in the new system, which is 5 levels higher than 1 in the old system, so she is an 8(+5). The top 15 rankings for female channelers would then go like this:
- 1(+12) e.g. Lanfear, Alivia
- 2(+11) e.g. Cyndane, Mesaana
- 3(+10) e.g. Nynaeve
- 8(+5) e.g. Elayne, Egwene
- 13(1) e.g. Moraine (pre-Genji), Siuan (pre-stilling)
Strength in saidin
Overall, men had a stronger upper-level on strength in the One Power than women; that is, the top-level male channelers were stronger than the top-level female channelers. Thus, there are 6 additional levels on top of the 72-point women's scale that men can achieve. These are numbered 1 through 6, but in order to reflect the fact that women could never reach that level, those 6 are notated with a ++. Thus, the comparison between the top 10 men's levels vs. women would be:
- ++1 e.g. Rand, Moridin, Rahvin
- ++2 e.g. Demandred, Logain, Aginar, Sammael
- ++3 e.g. Asmodean
- ++4 e.g. Be'lal
- 7 == women's 1
- 8 == women's 2
- 9 == women's 3
- 10 == women's 4
Note that, apart from the Forsaken, most of the men do not have strength levels given for them, though we can infer Rand's because Logain at ++2 is "one step below" him. The Companion explains that it's impossible to know up front how strong a man will eventually become, in general, and that their strength level grows in unpredictable spurts. And, while women tend to reach their full potential in about a decade, men can take much longer. Thus, for most of the Asha'man, who only had a few years at best to channel, there's no way to judge how strong they would eventually get.