Compass.rawVector returns zero vector on GalaxyS4

I have used script below

void OnGUI() {
        GUILayout.Label(Input.compass.rawVector.ToString());
    } 

It returns zero vector on screen.I don’t understand why it doenst work.Compass works well in tests of the phone.

Unity Version: 4.5.5f1
Phone:Samsung Galaxy S4
Andoroid Version:4.4.2

My problem is solved thank you.
I added the lines below to start function.

Input.location.Start();
Input.compass.enabled=true;

from Unity - Scripting API: Compass.enabled