Attackpoint calculates an alternative pace, taking the amount of climb into account. I presume it assumes start & finish at the same level? On a treadmill there is no downhill, so climb is accumulative. I've been adding an extra 50% climb to allow for the lack of downhill. Any thoughts?
Attackpoint always thinks of climb as accumulative (going downhill doesn't subtract from climb, just adds to "descent" which is not logged), and there is no assumption of start/finish at the same level.
if you want an accurate climb value from the treadmill, you can calculate that from your average incline. AP actually has a calculator for that on the add-training form. After you enter a distance, click the climb units (m or ft) and you can enter the incline in degrees or grade (grade is typically what treadmills display).
You can also make it a bit more complicated if you want to adjust for the lack of wind resistance. On a treadmill you are effectively always running with a tailwind, and you can compensate for the reduced effort with some extra incline (about 1-2 grade % points depending on speed). How you account for that in your logging is up to you. My personal preference is to ignore climb when the grade is 2% or less, or make a note of the incline setting in comments.