In the FAQ, battle mechanics are explained:

"For example, your pet's Courage and Strength sum equals 30, while your opponent has Constitution and Strength sum of 60. Your absolute damage value will be lowered by 50% (-1% per every 2% of difference)."

It may just be that I suck at math (which I do), but I think this could be explained a little better. In the example, the diffence is the same number as one of the sums and the percentage can be reached at least three different ways, so what's the correct way? Is the percentage being calculated from sum #1 or sum #2? How would you calculate it out with less perfect pairs, like 74 and 86, or 53 and 92?

There's a reason math classes usually work through more than one example of a type of problem before expecting the students to be able to work through any on their own, heh.

Try this

((Sum 2 / Sum 1) - 1) / 2 = Absolute damage value change
Where Sum #2 is larger than Sum #1

The idea is ((Sum 2 / Sum 1) - 1)  gives the percent increase of the lower sum to get the higher sum. 

so for 74 and 86, lets assume Sum 2 = Str + Courage and Sum 1 = Constitution + Str

(86 / 74) -1 = .162162 --> 86 is about 16% larger than 74
Since the damage value is decreased by half of that, thats ~8%. Sum 2 person deals ~8% increased dmg vs Sum 1 person.

and for 53 and 92

(92 / 53) - 1 = .73585
.73585 / 2 = .367925 ---> Sum 2 person is dealing ~36.8% increased damage against Sum 1 person.

And quoth the FAQ, no battle parameter can be changed by more than 50%. Correct me if my math is wrong.