This Percentage Increase per Level equation computes the increase to an attribute, a champion's abilities attribute, which increases a fixed percentage at each level.
This equation is used within the equation for determining all of the champions' base attributes at a specified level but can be used alone as in the example below.
Example: The movement speed of a champion is computed as a base constant with a % increase at each level. The champion called Ahiri's has an Attack Speed that is is given as 0.668 (+2% per level). 0.668 is the movement speed at level 1. The movement speed at each successive level increases by and additional 2% of the previous level and thus is compounded.
It is interesting to note that the computation of this percent increase for each level uses the Future Value equation from personal finance. Basically, Ahiri's movement speed compounds each level just like your money compounds in value in your savings account each month.