Hi. I have a problem using 3-axis accelerometer. I understand that the total acceleration is the square root of (x^2 + y^2 + z^2) but I cannot determine the direction of the acceleration. Say the device is at 45 degrees and is moved straight up, how can this vertical motion be detected. I can determine the angle/tilt of the device using trigonometry but cannot determine the linear motion in 3d. How can this be achieved, or is there any basic formula available. Thanks, Mark.