Calling MC within MC

I'm so close to getting an actionscripted project done.
But, I have a couple questions...

How would I call/target a movieclip within a movieclip from an actionscript on the root movie?

How does one center a movieclip in actionscript?

I seem to be running in circles.
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DocRee

FYI:The project is my version of the "raycasting" engine I mentioned in the "game pad" post.

Referring to a movieclip

code:

---

_root.rootChild.childOfRootChild._x = 5

---

Centering a movieclip

code:

---

myMc._x = Stage.width / 2

myMC._y = Stage.height / 2

---

Thanks, that works to an extent...
When centering a MC within MC it references close to the center, but not close enough.
Right now, it is just about 10 pixels [40 fips] left and up from center.
Is it possible that it is referencing around the center point of itself?
I have the cross hair at the uper left corner of the child mc and parent mc.
DocRee