How to calculate armor?

Well guys how do you calculate armor points?
For example if a unit has 20 armor, do you know how many % it takes from attacks?
BTW: I searched for it in the "Gameplay Constants" but only found a "Combat - Armor Damage Reduction Multipiler" whose value was 0.06. Hope this little information helps.

from battle.net:
Damage Reduction or Increases for Armor
For positive Armor, damage reduction =((armor)*0.06)/(1+0.06*(armor))
For negative Armor, it is damage increase = 2-0.94^(-armor) since you take more damage for negative armor scores.

What do those equations mean? I calculated it, using the .06, and got 1.2/2.2 = .55. So the damage reduction is 55%? Thus, if a unit attacked my hero for 100 damage, the unit would only do 45 damage? (100-55=45).
For the negative one, 2-3.45 = -1.45 (round, keep it simple). So a unit with -20 armor would recieve 1.45 more damage?
If I wanted to make each armor point negate 2 damage, what number would I use to do that, if possible.

For your last question, TaG.C, you can't do that with normal armour.

To OP: http://www.wc3campaigns.net/showthread.php?t=85631

I am about to improve the system, making it work with units affected by mana shield. I still need to find a better solution for spells like berserk and hardened skin. :)

~Daelin

im not completely sure, but if you raise .94 to the <armor you have>, you should have the percentage of damage that goes through armor. simple.