Detection amount of armor

[Drain Pipe]

I was working on a system to quickly and easily detect a units armor but I have come across an impass and there are 2 solutions which i am considering.

firstly, is there a way to use logarithms with the editor via .GUI or custom script (i found nothing amongst the .GUI commands)

Secondly, how does normal armor stack in-game, as in, what is the algorithm that determines the % of damage reduction based on armor?