I am confused about 'default altitude' vs 'absolute altitude' and the definitions of the two. Does anyone have advice about setting the 'absolute altitude' in the flight planner tab in mission planner? 

   If I check the 'hold default altitude' box for flight, will that be relative to absolute altitude, or does it recalculate based on APM power up altitude?  If I check the box for absolute, do I have to set absolute altitude for every waypoint as well?  What does the 'verify height' option actually do?  Is the number entered into default altitude the altitude that the APM will hold while in RTL mode, and what is this height based on? 

   I ask because I live at almost 8000ft ASL on a long slope up to 14000ft peaks and want to make sure it doesn't fly east and into the ground because I set it up it wrong. 

   ie, if I set default altitude at 5m, but the ground is at 2321m, then check the 'absolute alt' box, and check 'verify height' box how do those values equate to flight?   If I check the 'hold default alt' box, will it plow into the ground as it flies east and the ground comes up to meet the copter?  I know... lots of questions- lots of confusion.  Cheers for the clarification...