Accelerometer sensor channel

The accelerometer channel measuring the acceleration of the device. The three dimensional Cartesian coordinate system is used to illustrate direction of the acceleration as shown in the figure below. The x- and y- axes defines a plane where z-axis direction is perpendicular to the xy plane. When a phone is moving along an axis, the acceleration is positive if movement is towards positive direction and negative if movement is on negative direction. E.g. when a phone is moving along x-axis to the direction of -x, the acceleration is negative.