My quadcopter with APM 2.5.2 mod to 2.6

I say  after so many experience i had in build multirotor from KK2 , Multiwii and finally APM 2.5,

i found it APM 2.5 is a most easy and not much setting to tweak,
just plug in from the Arducopter guide motor and esc, arm it and she flies like a nice tame honeybird

The PID setting a perfect match for my clone Q450, and the flight feels much lighter n smooth compare to multiwii..

i found my quadcopter is easy to fly and handle, yet i havent test others function on my APM, and believe me APM had a 14 kind of flight mode, but the main important flight mode are

Alt Hold- Maintain altitude without need much input from throttle stick
Loiter    - it use GPS function to stay and hover one position
RTH      - the most important flight mode in my opinion if u fly LOS

ok after much awaited my GPS arrived from Hobbyking , and i connected to my APM 2.5,
and test loiter mode..but something not quite right ..the quadcopter tend to drift ramdomly, i try to recalibrating compass and accelometer but seems not solve my problem

after numerous time i look to RCGroup, they mention internal compass at APM 2.5 is not effective because it had interference from others electrical device such as motor, esc ,

i finally tooks decision to cut internal compass at my APM and put external compass and GPS..now my APM 2.5 officially become APM 2.6 hahahaha.....

what a surprise !! it works , my APM 2.6 now can loiter and do Return To Home...i am glad that finally i solve my problem