Expose Weakness

Expose Weakness is a talent from the Survival Talent Tree, which requires 30 Points in Survival and 5 Points in Lightning Reflexes, giving a 33%/66%/100% chance to Proc when you score a critical strike with your ranged attacks.

Assuming the hunter has 3/3 in the 'Exposed Weakness' talent, his ranged critical hits will have a 100% chance of proccing an Expose Weakness effect onto the target. The higher the agility, the better. Crit rating and agility is of the utmost importance to the Survival hunter. More crit = more proc --> nearly never ending Expose Weakness.

Expose Weakness is is also available as set bonus of Dragonstalker Armor. The 8 piece set bonus of the Dragonstalker Armor gives you a chance whenever you deal ranged damage to apply an Expose Weakness effect to the target. The Dragonstalker Armor Expose Weakness proc increases the Ranged Attack Power of all attackers against that target by 450 for 7 sec.

Formulas
Given the following definitions:

E = Number of points in Expose Weakness

C = Crit Chance (for a 30.0% crit chance, use 0.30)

A = Agility

S = Attacks Per Second (for white damage only, this is 1/Attack Speed, or 0.5 for a 2.0 attack speed)

The following two formulas will provide information the statistical average amount of attack power provided by Expose Weakness, and the statistical average percentage of time the debuff will be up on the target.

Percentage of time Expose Weakness will be on the target = (1 - ((1 - (C * 0.33 * E)) ^ (7 * S)))

Average amount of Attack Power given by Expose Weakness over time = (1 - ((1 - (C * 0.33 * E)) ^ (7 * S))) * (0.25 * A)

By using these formulas, it is possible to figure out whether it is worthwhile to move from only one point in the talent to two, or even to a full three points.