Rotating Menu

I am trying to set up a menu rotating. When you click on a button the movie clip rotates that button the the 90º position. I want the movie clip to rotate clock wise. It works fine with numbers smaller than 180, whenever I use a number larger that 180 the movie clip continues to rotate instead of stopping after reaching the set position. Anyone have some advise for me.

here is the action script ------------------------------
//Orb rotation code
Orb.onEnterFrame = function() {
this._rotation -= (this._rotation-turn)/12;

//button actions less than 180 works
Orb.btn1.onRelease = function() {
_root.turn = 90;

// more than 180 rotation never stops
Orb.btn2.onRelease = function() {
_root.turn = 225;