I'm sure they correlate: but the thing with correlation is that you can have correlation even when there are whole classes of situations where the relationship

I'm sure they correlate: but the thing with correlation is that you can have correlation even when there are whole classes of situations where the relationship doesn't hold. On the same os +drivers I'd be willing to believe that this measure is almost certainly useful (even there, it's not 100%). But it's exactly the kind of thing that a different way of, say... compositing... might the implementation to work a little differently, such that you're comparing apples to oranges. If BitBlt simply gets access a little earlier or later in the same pipeline and hey presto: you've got a difference in software that is meaningless in reality.