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.
Yes, it must be level when calibrating and it should be level when you turn it on to fly also.
While using a level is a good idea, be sure to check whatever level you use against an accurate level. Many sold today are cheap and not level at all. I bought a dozen like shown above and only 2 were actually level. Be sure and check them for accuracy or you're no further ahead.
I wish it were a case of calibration. I take off from a helicopter pad at work. I had to send it in to Yuneec for work. I haven't got it back yet, but they have been in constant co fact through out the process. Great customer service experience so far.
My first "H" had a camera that always very slowly tilted to the left. After about a minute it was at 45 degrees. Totally useless. I contacted Yuneec and they sent a courier to collect it. 4 days later I received a completely new "H". The second time it flew it, the camera tilted 45 degrees quite quickly. I have not contacted Yuneec again, as I feel pretty sure that it is ME. But what can I be doing wrong ? I have no problems with all my other models, DJI and Yuneec.
It even happens on my dining room table, so its not a dodgy flying area that I an using. I've done all the calibrations (many times).
It's not the lens inside the camera housing loose and turning, is it? I have no idea, I just remember seeing the upgrading camera videos on the 4K where they replace the lens, and I think it screws into the housing, so I just wondered.