"Resists Elemental Damage" mob affix?

How much is this, exactly? And is it the same universally? As in, does an Act 1 Zombie with this affix have the same resists as Uber Atziri (whom seems to have this affix, from what I'm reading on the Wiki)?

I'm ultimately trying to figure out Uber Az's resistances. But the Wiki seems to be making an assumption that I know one of the connecting dots, which I do not.

"Resists Elemental Damage" just means a mob has higher than zero elemental resistance. Not terribly useful.

Poedb lists Atziri's elemental resistances as 30%. If you don't want to blindly trust datamining you could try hitting her with a single-element hit from a skill socketed in a malachai's artifice. If for example you used Fireball with no added cold or lightning damage that would strip Atziri of exactly 30% resistance to cold and lightning damage which, if the value listed on poedb is correct, should change that "Resists Elemental Damage" to "Resists Fire Damage".

Thank you, sir! Good idea, too.