Mouse move start and end difference

1

i have built a navigation circle with a rotating handle
what i am trying to accomplish is

on mousemove
if the rotation end position is greater then rotation start position
the links movieclip go to the next frame other wise it goes to the previous frame

[COLOR=Red]in red is where i’m having trouble[/COLOR]

rotFun = function () {

var dx:Number = _xmouse-this._x;
var dy:Number = _ymouse-this._y;        
var radians:Number = Math.atan2(dy, dx);
var degrees:Number = 360*radians/(2*Math.PI);

    this._rotation = degrees;

[COLOR=Red] if(this._rotation++){
_root.dial.links_mc.nextFrame()}

else{    _root.dial.links_mc.prevFrame()

}[/COLOR]

}

knob.useHandCursor = true;
knob.onPress = function() {
this.onMouseMove = rotFun;
}

knob.onRelease = knob.onReleaseOutside=function () {

 _root.dial.knob._alpha = 100
 delete this.onMouseMove;

};