Although not right down to the penny, I think the 'general idea' is to find your two highest skills' rank then plot them on the chart.
For example, I have a Rank 7 windmill and Rank E defense. Rank 7 windmill is ~120 CP while Defense E is ~60.
That means the CP from my skills comes to 180 CP in all. Note that this doesn't put stats into play, but you get the general idea on what skills to worry about. Folks worried about their combat power will want to avoid those skills that really JUMP down those numbers, like Defense. On the other hand, Ice bolt isn't that bad to touch on.

Ever felt like this some days?