That thing is a fairly useless control. If you are sailing with a spin blow it off all the way to the back or have the thing removed and have a clew plate installed with about 5 holes in it (if your sail design will allow it).
If you sail primarily with main and jib only, leave the thing centered and forget about it.
One thing to note.... If you are sailing the boat fast and happen to flip over, try not to fall on this piece of hardware. It will fold in half like a taco!! And getting a new one is next to impossible. Also take the thing off the sail every so often and be sure there is no corrosion on it (in the center). I have bent one from sheeting too hard. I actually put two traveller cars on the track to help spread the load.

AJ
Express 6.0