Percentages in Warcraft tend to be very straightforward. Remove the % signs and look at it again:
You have 30.54 Block. You gain 100 Block. You now have 130.54 Block.
I'm seeing some weird numbers with shield block, and I'm not sure if I'm interpreting the numbers incorrectly or if there's an error in the tooltip. This is what I see as my baseline block:
And this is what it shows when Shield Block is up. Block chance 130.54? And shouldn't my damage blocked double?
It appears to me that the % block is incorrect--it's not increasing the chance by 100%, but more like 500%. It's entirely possible this is just a tooltip error and the spell is actually working as intended.
It adds 100% to your shield block rating, it's not multiplicative. As for the block value, I believe shield block affects your block value before the "Shield Mastery" talent.
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Im not sure what u mean with it increasing 700%? 30.54 to 130.54 is 100%. It doesnt mean doubling 30.54% it means adding 100% block rating to it. And i forget why it doesnt actually double block value but it doesnt take something into account when it does double
I guess I was interpreting the "chance to block" in the tooltip as directly affecting block rating. Thus, increasing the block rating by 100% would not result in a 130% chance to block. But of course, the tooltip refers to affecting the resulting percentage to block directly.
For the block value it adds the unbuffed blockvalue like this:
unbuffed blockvalue * (talents + glyphs + metagem) = what you see
Now when you press shield block u get:
unbuffed blockvalue * (talents + glyphs + metagem) + unbuffed blockvalue
So it's not really doubling your blockvalue unfortunatelly.
As a sidenote:
the imp revenge talents works the same way, as in only improving the base damage of revenge, not the ap part.
Dunno if it's an oversight on blizzards part or actually intended. Maybe someone can report it as a bug on the US ptr since it's my firm belief they do read that more then the EU one no matter what they say.