Rotation around simulated registration point?

Hi, I want to have arm movement such as the forearm rotating about the arm where the elbow should be the problem is the registration point is at the shoulder for arm. I want the forearms registration to be constantly equal to a simulated registration point where the elbow should be as the arms registration point would be at the shoulder. I need to do it WITHOUT NESTING(a movieclip within another) is it possible.

i tried useing a constant distant between the two clips but it doesnt work. dont know I I have to use trigonometry or not

I’m actually trying to do this in Director,so nesting wouldnt work

I think in brief what I trying to accomplish is
onEnterFrame=function(){

arm._x=shoulder._x
arm._y=shoulder._y

------------------problem----------------------------------
arm._x=simulated_x(where elbow would be)
arm._y=simulated_y(where elbow would be)
}

Thanx, sorry for any spelling mistakes