Was looking for extra sources of physical->pierce conversion and I found the Sinister prefix on rare swords which gives another +%Armor Piercing stat in addition to the usual one on swords and some axes. How does it work? Does it apply to both weapons (like Blessed Whetstone) or just the one it’s on? How is it calculated in the mix of the actual %armor piercing stat on swords, a blessed whetstone, and Blades of Nidaan (all of which I have)?
AFAIK things that increase armor piercing % act as a multiplier on the existing armor piercing a weapon has. You have +100% armor piercing and a sword with 25% armor piercing, it now has 50% armor piercing. Increased armor piercing on a weapon like from the component or the affix are local I believe, just like flat damage or lifesteal.
Except that Blessed Whetstone does cover both weapons, so there are anomalies. Hopefully Nine, Ceno or the like will weigh in here.
Does it? That would seem to be the odd one out, as I’m pretty sure Sinister is weapon specific. Haven’t played a dual wield character with a focus on piercing in a while though.
>I’m some kind of authority
>meme arrows
I used to think Blessed Whetstone’s +% Armor Piercing was localized but no, after some testing, it is in fact global.
E: I’ll have to test Sinister, then.
Clearly post count > join date :p.
Not always 
Though I did garner some attention awhile back when I was a bit more argumentative and inclined to post frequently.
Not the greatest attention mind you.
Sinister like Blessed Whetstone works on both weapons.
Glad I was able to help contributeto the community’s body of knowledge. Don’t worry about crediting your sources; we’re all here to make things better for everyone!
My sources are I tested afterward to confirm, but yes, thanks.
So, confirmed? I only have one Sinister in my entire history of playing this game, but the bonus is quite high.
If you have one its easy for you to test and see for your self, equip it, check your weapon attc toll tip breakdown and do the math 
If I was good at math I wouldn’t be asking half of my questions. But really it’s more that the mechanics of this game can be complex and confusing. I don’t know how to interpret the tooltips accurately, sorting out between the flat damage sources, the % bonuses, and the piercing conversions, because I don’t know the exact order the engine performs the calculations in, whether a particular conversion is additive or multiplicative, etc.
Come on its not that complex, specially this part with armor piercing, Im sure you can do it 
Look, unequip all your gear with some kind of conversion on it. Equip some common sword with lets say 33% Armor piercing, check weapon atc tool tip breakdown to see your amounts of phys and pierce dmg. Than in other hand equip your sword with sinister prefix, and check your tool tip again, you should, see depending on how much % to AP your sinister prefix have, change of your dmg ratio. If sinister works on both hands it will skyrocket you pierce and your physi dmg will be probably lower or minorly higher than when you had only one weapon equipped. Compare ratios of phys and pierce dmg when you had only one sword equipped with new ratios if you are not certain.