Hi, please don't hesitate to reply to either of my paragraphs. Or ask for clarification. The first paragraph descibes the basic problem, and the second one is more indepth. I'd be happy if I could get just the first one working. I'm working on a project were a two-axis accelerometer will be mounted to a helmet, and worn by a user. Currently I have the accelerometer mounted with both axes parallel to the earth. The problem I'm working on, is having the user pan their head(moving parallel to the earth), left or right, and calculating the angle. My approach is to calculate the distance in each direction(x and y), using d = d0 + V0*t + 1/2 * a * t^2, and then take the inverse tangent of these two results. Then store the new velocity, using v = v0 + a*t, for use in the next calculation. Does this sound like a good approach, or is there perhaps a better way to do it? As it currently is, I can calculate the amount the user rolls or tilts their head, since the measured acceleration changes as the axes become more or less perpendicular/parallel to the earth. i.e. When the X-axis is perpendicular to the earth it experiences +-1g of acceleration, when it is parallel it experiences 0g. So these values can be used directly. However this approach doesn't work for panning, since the movement is parallel to the earth. Ideally, I'd like to be able to calculate the amount the user pans their head even when their head is tilted and rolled. Any advice or ideas would be greatly appreciated.