Gesture recognition with two 3-axis accelerometers

This paper is talking about using two digital accelerometers to recognize the gestures composed of thumb and forefinger. Two accelerometers were placed by parallel with y-axis and z-axis of accelerometers toward opposite direction. Then add up two accelerations of the same axis from different accelerometer to eliminate the anti-gravitational acceleration. Integrate the pure acceleration to find the velocity and uses the curve of velocity to recognize the gestures.