onMouseMove Question

I am using this code to slide through frames in my swf by waving my mouse back and forth:

_root.onMouseMove = function() {
moveForward.gotoAndStop(Math.ceil(_xmouse/10)); }

I would like it though to start from east to west insted of the other way around so when i move to the east my frames go forward. i cant figure it out at the moment. would appreciate some help. thankyou in advance