how does armor, magic resist, armor pen, and...

[quote=turingexp]What does 1 point of armor equate to? Same with magic resist, armor pen, and magic pen? At first I thought that 1 armor nullifies 1 point of attack damage, and that 1 point of armor pen nullifies 1 point of armor. But that seems too simple. thanks.[/quote]

[quote=Luther3000]http://leagueoflegends.wikia.com/wiki/Magic_resistance Tl;dr: Each point of Armour/MR reduces incoming damage by a percentage, but it's not as simple as 1 point = 1%. The more you already have, the less percentage reduction you get for stacking more. For example: 25 Armour/MR = 20% 100 Armour/MR = 50% 150 Armour/MR = 60% 300 Armour/MR = 75% If you hover over your Armour or MR while playing, the tooltip will actually tell you what percentage of damage you are currently blocking. Penetration works exactly the way you think it does.[/quote]

[quote=turingexp]so there is clearly a point where stacking armor becomes inefficient in terms of gold/damage reduced.[/quote]