I have a flash script, i added one move clip via addChild, my movie area is 500x400
and the movieClip i aligned to center. But when am trying to set the size with in browser its not aligned to center. all my calculations are getting wrong.

```
package {
    import flash.display.*;
    import flash.display.Stage;
    import flash.geom.*;
    import flash.net.*;
    import flash.media.*;
    import flash.utils.Timer;
    import fl.motion.Color;
    import flash.events.*;
    import flash.text.*;
    import flash.system.LoaderContext;
    import flash.system.Security;

    public class main extends Sprite {

        public function main(){
            trace("Hello");

            var btn:_Button = new _Button();
            btn.x= (stage.stageWidth - btn.width)/2
            btn.y= (stage.stageHeight - btn.height)/2
            addChild(btn);
        }
    }
}

```

Here is my code