Mathematics and easing

hello all,
I need some math help I think…
I’ve built a code to cyclically move a scene on the bottom of my stage; I’ve done this to make a slowing-and-stop-easing effect at anytime the command will arrive. The entire scene mc is _x long something like 6000 px
The whole code goes in this way:

  1. importing on the stage (with attachMovie) a mc with this code inside:

onClipEvent(enterFrame) {
_parent._parent.fondo_mc._x -= countermovement;
if (_parent._parent.fondo_mc._x <= -5800) {
_parent._parent.fondo_mc._x = -30;
}
}

  1. In the main timeline this code:

var c countermovement:Number = 6;
attachMovie(“procemuovifondo”, “procemuovifondo”, 5000);

function slowAndStop () {
procemuovifondo.onEnterFrame = function () {
if (countermovement > 0) {
countermovement --;
trace (“counter” + countermovement);
} else {
removeMovieClip(procemuovifondo);
}
}
}

The code goes right, but I need to improve it.
Now there is just a variable, I tought to use two vars to implement the whole code in a setInterval, but maybe it’s unuseful, and actually I can’t use it in the right way.
Second issue: actually when slowAndStop function is called the scene slow too fast, if I take it to 15 it slow better but the scene is running too fast…

The best would be that the scene slow down and stop following:
A) a temporal variable (and I can try to implement it with setInterval, that for istance is a cycle)
B) an indipendent moving variable, so that on one side I set the speed, on the other side I set the slow-and-stop in a matter of time with countermovement.

I also tried to use a second variable:
var counter:Number = 15;
// set the _x increment
var countermovement:Number = counter/2;

but the scene slow and goes backward a bit :ogre:

thanking you in advance