Ability Increase (Ex) 2 per
An eidolon grows larger muscles, gains faster ref lexes, achieves greater intelligence, or acquires another increase to one of its abilities. Increase one of the eidolonís ability scores by +2. This evolution can be selected more than once. It can only be applied once to an individual ability score, plus 1 additional time for every 6 levels the summoner possesses. Source: Advanced Player's Guide
By the way, explain this: Does this mean that I can only take this every 6 lvls?
or does this mean that I can only take it once on a certain score and cannot add another to that score for another 6 lvls?