I've been doing some math for the dragonhunters in my guild and I had to know which traits are additive and multiplicative for dps. Whenever I equiped the Zeal traitline my damage got crazy until I realized that zealous blade is more than just 240 power and 20% cooldown reduction
The trait used to give a conditional 10% modifier, but got changed 6 months ago to instead grant some extra power. However with some testing its easy to realize that the trait still gives 10% extra damage
An easy way to confirm this yourself is to
0) Strip yourself completely naked and equip an ascended greatsword without any selected stats (now you have 1000 power and 5% critchance)
1) Unequpid all traitlines except for Zeal. (Dont pick any traits outside of the mandatory minors in Zeal)
2) Hit the golem with Leap of Faith until the ratio between your highest and lowest strike is close to 1.105 (It should hit for between 503 and 556 damage)
3) Equip Zealous Blade
4) Hit the Golem until the ratio between your highest and lowest strike is close to 1.105.
When you gain 240 power, Leap of Faith should hit the golem for between 624 and 689 damage. (Basically you take your Damage with 1000 power, divide it by 1000 and multiply it with 1240.) However you will see hits between 686 and 758 with zealous strikes which is 10% higher than intended.