Yesterday I was at the Microsoft Technet/MSDN sessions in Rotterdam (The Netherlands) talking on this subject with two Dutch Microsoft developers and although they offered a few possibilities, they didn't have the answer anymore than non-Microsoft developers.
Well, I give up (no, I don't, knowing myself). What caculation is used? Moving average? Data left to copy divided by the speed at that moment?
Will I ever find the programmer that developed that routine. Stay tuned