Wheel of Fortune action

I am trying to create an action that enables a user to spin a disc. That disc must have velocity action on it. I’ve so far been able to get it to rotate correctly with the velocity. However, whenever the rotation hits 180, the disc starts spinning erratically forward: I think it’s advancing 360 degrees forward.

I’ve never been able to fully understand the movement equation to analyze where the equation is making the disc spin out of control. So if anyone can help, I would be grateful! Here’s the setup -

On the main timeline exists two movieclips ‘arrow’ and ‘disc’, and also on the same timeline is the following code:

var rotate = 0;

right.onPress = function() {
	this.onEnterFrame = function() {
		rotate +=5;

right.onRelease = function() {
	delete right.onEnterFrame;

Inside ‘disc’ is the following code:

this.onEnterFrame = function() {
	this._rotation -= ( this._rotation - _root.rotate ) * .05;
	trace("circle's rotation value: " + this._rotation );

I’ve also included the flash file at the following address if needed: