User blog comment:Slashingstrike/AP Item for Tanks/@comment-25235491-20161026105240/@comment-4636093-20161027100359

That's not actually the equation for armor protection.

For one thing, having 50 armor doesn't equal 50% protection. 100 armor equals 50% protection.

The equation is: damage taken = 100 / ( armor + 100 )

This means that the damage reduction you get from armor isn't linear. Having 50 armor means you take 66.6666% damage from physical damage, but adding another 50 armor means you take 50% damage, adding yet another 50 armor means you take 40% damage, another means you take 33.3333% damage, etc.

As you can see, the protection you get from adding 50 armor gets lower and lower every time.