[a_Guest03]

2.7 * Skill + 4/3 * Offense + 0.915 * (Strength - 75) + 8

That was offered in a google group search, found by var1ety. UrineTrouble tested values

Stats: Level 36 iksar SK, 575ATK, 180offense, 80STR, 119 skill
Live value: 575
Equation value: 573.875
discrepency: -2
Same guy, 0 skill
Live value: 255
Equation value: 252
discrepency: -3
Same guy, 185 skill
Live value: 752
Equation value: 752
NO discrepency

Stats: Level 1 DE wiz, 0 offense, 60 STR, 0 skill
Live value: 10
Equation value: -5.725
discrepency: -15
We don't need to cap the ATK rating at 10, we need to cap a portion of the function. If STR < 78, use 78 as the value in place of strength.
Adjustment equation value: 10

Stats: Level 1 DE wiz, 0 offense, 75 STR, 0 skill
Live value: 10
Equation value: 8
discrepency: 2
Theory verified - ATK low value capped at 10.

Ran this through a lot of live data:
Verified within 5 ATK for 99% of data
Verified within 2 ATK for 95% of data
Verified within 1 ATK for 68% of data

Another condition was found, based on the DE problem listed above - (old way of solving was to cap ATK rating at 10)

Level 57 enchanter, 64 STR, 95 offense, 0 skill
Live value: 138
Equation value: 124
discrepency: -14!
Explanation - We don't need to cap the ATK rating at 10, we need to cap a portion of the function. If STR < 78, use 78 as the value in place of strength.
Adjustment equation value: 137

More to come.