What happens with mine is that it calibrates to the surface you are on. For example, if your UAV is leaning 45 degrees to the left, and you let it go through calibration, your in flight images will be 45 degrees to the right when in level flight. (I use 45 degrees, but I don't know if it actually will calibrate that far tilted).
I bought a bubble level - the kind with a dome, and a bubble that centers in the circle at the top when the surface is level. I attached it to the center of my case, and use my case as my launch pad for the Typhoon. Before starting the Typhoon, I use Styrofoam wedges I made from some packing material, and lift the case on one or two edges to get the bubble level centered.
When I start the Typhoon, it is now on a level surface, and my camera calibrates perfectly level.