After flying roughly 90 minutes total after five flight sessions, I find myself looking a bit more at the Ipad as my confidence has increased. Coming from an aviation background with many different altitudes that we think about - and all their acronyms and definitions - I just want to be sure I am getting this right. The controller captures your home position and calls this altitude zero in telemetry. Subsequent indicated altitude of the copter as it ascends and descends is how far it is vertically above this zero point. Did I get that right? What happens if one takes off from a hilltop and decides to land in a valley below, well beneath the zero point?