Stable-Hover sets the Hover height and maintains that height.
Alt-J and Alt-K adjust the Hover height down/up respectively. Watch your altitude gauge as you press the keys,
it jogs up or down 10 ft or 5 meters depending upon whether you are blue or red.
Pop-Up works Up and Down from the Hover height.
Pop-Up toggles Up 20m on the first keypress, then Down 20m on the second keypress.
Does that clear up the functions?
Is blue feet, and red metres?
In the Apache, it was going up and down by around 70 marks (whether that's feet or metres). But that was after I'd already used the height adjustment. I'll try it again, and keep track of what I'm doing. i was just playing around quickly with it.
p.s. I'm a software tester, and the fact I think I've spotted an issue and not properly recreated it is bothering me. I'll do it justice next time I'm on