Android - ช่วยอธิบายโค้ด Sensor Gravity Android นี้้ทีครับ ไม่เข้าใจ

//package app.ken.testsensor;
//
//import android.app.Activity;
//import android.hardware.Sensor;
//import android.hardware.SensorEvent;
//import android.hardware.SensorEventListener;
//import android.hardware.SensorManager;
//import android.os.Bundle;
//import android.widget.TextView;
//
//public class MainActivity extends Activity implements SensorEventListener {
//    private SensorManager mgr;
//    private Sensor accelerometer;
//    private TextView text;
//    private float[] gravity = new float[3];
//    private float[] motion = new float[3];
//    private double ratio;
//    private double mAngle;
//    private int counter = 0;
//
//    @Override
//    public void onCreate(Bundle savedInstanceState) {
//        super.onCreate(savedInstanceState);
//        setContentView(R.layout.activity_main);
//        mgr = (SensorManager) this.getSystemService(SENSOR_SERVICE);
//        accelerometer = mgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
//        text = (TextView) findViewById(R.id.textView);
//    }
    @Override
    protected void onResume() {
        mgr.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_UI);
        super.onResume();
    }

    @Override
    protected void onPause() {
        mgr.unregisterListener(this, accelerometer);
        super.onPause();
    }

    public void onAccuracyChanged(Sensor sensor, int accuracy) {
    }

    public void onSensorChanged(SensorEvent event) {
        for(int i=0; i<3; i++) {
            gravity [i] = (float) (0.1 * event.values[i] + 0.9 * gravity[i]);
            motion[i] = event.values[i] - gravity[i];
        }
        ratio = gravity[1]/SensorManager.GRAVITY_EARTH;
        if(ratio > 1.0) ratio = 1.0;
        if(ratio < -1.0) ratio = -1.0;
        mAngle = Math.toDegrees(Math.acos(ratio));
        if(gravity[2] < 0) {
            mAngle = -mAngle;
        }
        if(counter++ % 10 == 0) {
            String msg = String.format(
                    "Raw values\nX: %8.4f\nY: %8.4f\nZ: %8.4f\n" +
                            "Gravity\nX: %8.4f\nY: %8.4f\nZ: %8.4f\n" +
                            "Motion\nX: %8.4f\nY: %8.4f\nZ: %8.4f\nAngle: %8.1f",
                    event.values[0], event.values[1], event.values[2],
                    gravity[0], gravity[1], gravity[2],
                    motion[0], motion[1], motion[2],
                    mAngle);
            text.setText(msg);
            text.invalidate();
            counter=1;
        }
    }
}