Question about turtle_tf transformlistener

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Hi, recently I am learning tf package. I have read the tutorials, but have a small questions concerning the source code of transformlistener, which is: "vel_msg.angular = 4 * atan2(transform.getOrigin().y(), transform.getOrigin().x());" in the line 35. Why dose it need to multiply 4 here? For the aim of more quickly tracking? I know the scale value for keyboard control is 2, but it should be irrelevant to this, as this is calculated from the coordination. Appreciation for any help!