As of the more recent versions of ArduPlane, the firmware no longer does an automatic level on startup. Instead, that has become one of the initial startup steps when installing it in a new plane.
In the past, I have glued a bubble sight onto the rear spar enclosure and used that as "level". Recently, someone else said they use the inside floor near the CG line. Both seem ok, but both are different. I just looked at the wing and the underside is angled slightly node-down with my bubble level technique.
Does anyone have, or want to offer, their way of determining X-8 airframe "level" for the purpose of setting up the APM?