I've set my ArduPlane level to manual and have set it on a known level surface, this way I should have the plane at the same level each time I fly. (IMO, to set the level before each flight seems terribly inaccurate as you are just 'eyeballing' it and there is no way you'll get it exactly the same before each flight unless you use a spirit level each time which is just impractical).
There is also a parameter (TRIM_AUTO) which remembers your trim values at each mode switch with the caveat that you must only switch when the sticks are level.
In Manual mode with my trimmed plane (trimmed for level flight), the CH2_IN is 1381ms and CH2_OUT is 1381ms.
1) when I switch to Stabilize or FBW-A with TRIM_AUTO on then the CH2_OUT goes to 1421.
2) with trim auto off, Stabilize is 1393 & FBW-A is 1321.
All have noticeable and different effects on the flight pitch attitude of the plane so I cannot get consistant results which is frustrating.
I'd expect in case 1 for the CH2_OUT to follow CH2_IN and in case 2 for Stabilize & FBW-A to be the same.
Why the discrepancies?