Killer Trait - I am confused

[Brother Sapo]

d20pfsrd wrote:

Killer

You made your first kill at a very young age and found the task of war or murder to your liking. You either take particular pride in a well-placed blow, or vile pleasure in such a strike as you twist the blade to maximize the pain.

Benefit: You deal additional damage equal to your weapon’s critical hit modifier when you score a successful critical hit with a weapon; this additional damage is added to the final total, and is not multiplied by the critical hit multiple itself. This extra damage is a trait bonus.

I have no idea how to use this. I am building a Zen Archer for PFS. So, suppose I score a critical hit with a long bow (20, x3) How does this trait affect the critical hit damage?

Ordinarily, if I confirmed a crit, I would roll 3d8 for a long bow. If the bow had a +1 strength rating, the damage wouldbe 3d8+3.

[kingpin]

As I understand it, you would do an extra 3 damage as your crit modifier is x3.

[Lathiira]

Add the value of the weapon's critical hit multiplier to the damage you do. For your longbow, a critical hit does 3d8, plus 3 for the trait's bonus. If it were a scythe, you'd add 4; for a rapier, you add 2. If we use the bow with the strength rating, you'd do 3d8 +3 for the strength rating +3 for the trait.