Position of mc's

Helloo…
Look here for my swf.
When you drag the mouse over the line a mask is pulled down by a script. That mask is a big box. The same script is put onto the line. I thought they would be synced, but as you can see the mask isn’t following the line correctly.
As far as I know this has something with the positioning of the mask and the line in the mc’s. The script looks like this:

onClipEvent (load) {
	_root.newpos = "null";
}
onClipEvent (enterFrame) {
	var acceleration = .25;
	var current = this._y;
	if (_root.newpos > current) {
		distance = current - _root.newpos;
		this._y = current-(distance*acceleration);
	}
	if (_root.newpos < current) {
		distance =  _root.newpos - current;
		this._y = current+(distance*acceleration);
	}
}

The var newpos is generated when _ymouse < 100. How should the mask mc be placed? Or is it a better way to do this scrolldown thing to show something that wasn’t shown before. I don’t want to use motion tweens…

Someone? Please??