@Override
    public void onDestroy() {
        initDisposable.clear();
        if (tts != null) {
            tts.stop();
            tts.shutdown();
        }
        wakeLock.release();
        Log.w("SpeechService - WakeLock released");
        super.onDestroy();
    }
Return distance required to be moved based on overall distance.<br>

@param distance in km
@return delta in km
main/src/main/java/cgeo/geocaching/speech/SpeechService.java