Another thing to take into consideration if you need an exact volume is how the metal is bent. If the pipe is not mandrel bent, then you're going to lose volume in the pipe curves. Not much, but if you need something exact, that might be a varible to consider.
I'm not sure whether or not the AEM is or not because I don't have one and have never seen it posted. I would assume it is because of the company, but I could be wrong. Just something to ponder I guess.