Quote - "*Whatever their definition of altitude is, it should be

1. well defined in the manual.
2. Changeable by the users without adding and deleting a sea plane
3. Consitant. All altitudes defined relative to an arbitrary point, or all defined relative to sea level. Defining it randomly is a bug or a flaw in their treatment of coordinates.*"

1- Agree. Still, no flaw in the program, just in the documentation.
2- Disagree. Just do whatever's easier for the user.
3- Disagree. It's not random.

Regarding the option to define the sea level, I found it now. It's in "Units & Coordinates".