User blog comment:Willb32764/Health vs Armor/Magic Resist/@comment-6016076-20150710084448/@comment-24603390-20150711093628

The Health and MR/AR are you CURRENT Health or MR/AR, and so therefore include you base + scaling + items etc. As you have described, the value of health and AR/MR change based on thier current values, which is why this is a graph of current Health/MR/AR.

The y intercept of 750 is due to the formula for effective health being: Effective Health  = Health*(1+AR/100). This results in a 100 times ratio between armor and health. Next the 7.5 comes from the different is price between the two stats. 7.5*100 = 750, the value for the intercept. If you would like the full formula used, i can find it for you.

As mentioned above, the graphs are made without taking into account armor pen etc. If your attackers had 35% armor pen for example, armor effectively becomes less gold efficent, and so the values 7.5 and 750 would need to be modified to  ~11.5 and ~1150 to account for this penetration (7.5/(1-.35)=11.538)

As there are two variables that effect effective health (HP and MR/AR), 2 dimensions is exactly the number needed to model it.