Active Track is new to me (last Phantom I had was a P2V+). I've understand that drawing a box around a subject, and clicking the OK is necessary, but after that, there is a horizontal line with rotation arrows on either end - and a zero value. I can slide the ball from the center to either extreme, but what does that do? I tried it once, which seemed to swing the MP to the respective side, but then the active tracking stopped following the subject.