keep the azimuth when the tablet goes from landscape to portrait orientation

Question

I would like to compensate the roll from orientation of my tablet. I work with azimuth,roll, and pitch. I want to use just the azimuth (which the angular position from the center of my installation). When I go from landscape to portrait orientation, (means the roll is moving), the azimuth values go crazy and gives wrong values. What would be the best way to compensate the roll values in order to not alter azimuth values? thanks