OK moving past your obsession with the altitude thing if you want to use negative values you need to change the default minimum height setting under settings | movement parameters. Once set to a negative value you can specify waypoint altitude below the reference point.
So your first waypoint will have an altitude of +30, your second would be -50 and when you engage ensure you set the take off location or the operator as the reference point assuming you and the Mavic Pro are standing on top the 100 flight cliff and do not intend on moving if you use the operator.
However, the above is pretty advanced and as you say you are taking your first steps. So don't do this until you are 100% happy with the use of the app. Like I say, start with orbits and ziplines and practise disengaging either in app or by switching flight modes.
Have to say I have never used negative values, I always use the default minimum altitudes and start from the ground up. Finally there is always more than one way to skin a cat so you may find other ways to do the above, thats the fun of it!
Thank you for your in-depth reply. Much appreciated.
My "obsession" stems from almost 40 years as an aviator, first as a fighter pilot with an ejection under my belt, then as airline F/o, Captain and former TRI who has repeatedly committed himself to make sure that the concepts associated with these definitions were made clear, in order to make the skies safe for everybody.
For all practical purposes UAV are flying machines that have to comply with provisions set out by such authorities as the FAA and EASA.
As such, it is not up to manufacturers or software developers to come along with personal definitions for long established aeronautical terms and concepts. Not obeying to a defined lexicon for a particular activity can lead to unwanted results, and, in aviation's particular case, those results can be nasty.
I've now come to conclusion that Auto Flights's Autopilot is not very effective in this regard.
I've also downloaded Litchi and, the simple fact that it has a desktop planning tool - "Mission Hub" - where any created waypoint immediately shows overall elevation and height difference from the starting point, makes it a more adequate approach for my needs.
I will keep AF Autopilot and will certainly explore it in depth in the future but, for the moment, I will train with Litchi to make it the tool of choice for my next project.
Again, thank you so much for your help and I hope I can keep counting on you guys in the future to help me better understand Autopilot.
MK