Ok, lets see if I can clarify the whole "correlation" thing. I can only speak for my self..... I was taught that, as many have already stated, your A line is your gold standard- that IS your accurate B/P- provided it zeroed appropriately, ect,ect. By "correlating" you are checking to see how close your cuff is to your A line- does it always run 10 higher, is it all over the place?? Then.... if something happens to your A-line- you kinda have some idea where you stand until you can fix your A line problem.
I guess what I am trying to say is that I think when people use the phrase "correlate" they not speaking about the accuracy of the Arterial pressure, but the accuracy of the cuff as compared to the arterial pressure.
Does that make any sense? Maybe I'm just rambling???