A.T, thanks for taking the time to read and reply to my post.
I tried calibrating with the arm pointing down and had the same problems. The extreme case makes it easiest to visualize. Extreme case: user mounts the device at 90 degrees (i.e. the x reading, rather than the y reading, runs...
I'm so over my head that I don't even know how to ask this, but here goes...
The accelerometer in my device (an iPhone) gives an x,y,z vector that points to Earth. I'm using these values to determine the angle of the device relative to the horizon. Visualize a user aiming the device at a...