title: Alpha value in removing gravity from acelerometer data
body: <p>I came across this solution to remove gravity values from raw values of an acelerometer but I can't understand why <code>alpha = 0.8</code> and not just 0.997.</p>
  
  <pre><code> public void onSensorChanged(SensorEvent event)
   {
        // alpha is calculated as t / (t + dT)
        // with t, the low-pass filter's time-constant
        // and dT, the event delivery rate
  
        final float alpha = 0.8;
  
        gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];
        gravity[1] = alpha * gravity[1] + (1 - alpha) * event.values[1];
        gravity[2] = alpha * gravity[2] + (1 - alpha) * event.values[2];
  
        linear_acceleration[0] = event.values[0] - gravity[0];
        linear_acceleration[1] = event.values[1] - gravity[1];
        linear_acceleration[2] = event.values[2] - gravity[2];
   }
  </code></pre>