The instance clip and its own coordinates

I have a movieclip (imported from library) in main stage, with mc._x you have the x position in the main stage. But I wnt to know its position in its OWN corrdinates center. When you created the movieclip in authoring way, with drawing tools for example, you create this object in its own stage, and the position is referenced with a little cross in the middle. I want that numbers, how I can get them with code in the main timeline???
Greetings
:dilbert: