Can iPhone 6 tell if a surface is horizontal? I can launch the Compass app on my iPhone 4 and it can tell if the surface I'm placing it on is perfectly horizontal, or it's bending to any direction. Given iPhone 6's sticking-out camera, can it still measure such things?
Yes you can. 


Find a surface that you trust to to be level
Open the compass/spirit level app and place phone on it
Tap the screen while phone is placed on the surface - this will recalibrate the accelerometer reading on your iphone6 implicitly
taking into account the camera bump as well.
Go measure the things you want to measure :)


There is a catch to this, as it does assume that the surface is wide enough to place an iPhone 6 down with the camera bump touching the surface.