I cannot find that calculator either, and I, like you, remember seeing it one time.
FWIW, on my vehicles, I do a drain and refill x3 and I feel comfortable doing that, although I know it is not 100%. It is still close enough for me. Any more than that, and I think doing this is a big waste of fluid and you might as well go hook up to a T-tec at that point.
Lastly, when I owned a 2006 Saturn VUE, the Honda and Saturn dealer (tranny on these is a Honda AT and is not recommended to be flushed as Honda thinks it could cause problems), they told me that the standard procedure is to do a 3x drain and fill and it would get you to what they consider a full ATF fluid change. BOTH dealers told me this and if I didn't do this myself, would've charged well over a 100 bucks which is crazy.