Damage Calculation

Just to say, I'm starting my game with low stats, with the possibility that stats will never get past 150.

So, I'm trying to work out how I want my damage to look in my game, so I set my enemy defense to 6 and my actor attack to 5, and fire up a battle test expecting to see about 5-10 damage. Instead, what do I see? 34 (average) damage..  Then I changed enemy defense to 15.. 17 damage. So I finally set it to 20 defense and now the damage is 0.. sometimes 1.

What I'm requesting is this:

a script that allows me to make my own formula. Basically, what I want with that is to make attack a direct determination of damage. If you have 11 attack, you do 10 damage, for example, against an enemy with 1 defense (since by default you can't have 0) If you have 5 attack against an enemy with 5 defense, you do 1 damage.

Basically: (Attack - Defense) + 1 = Damage. (this works for melee skills as well) The final damage can never be 0.
And for spell damage: (Actor spi - Enemy spi) + random # that I can specify = Spell damage

Any questions, or if you need further explanation, please ask. And, thanks in advance.