_rotation?

Ive this problem with rotating an object.
What I want to do is rotate an object to
108 degrees than rotate it back to 72 degrees.

So what I did was:
[AS]
onClipEvent (load) {

// set speed
rotationSpeed = 2;

}

onClipEvent (enterFrame) {
// start the motion
_rotation += rotationSpeed;

// rotate back when gone to far.
if (_rotationSpeed >= 108) {
rotationSpeed *= -1;

// stop at 72 degrees
if (_rotation == 72) {
_rotationSpeed = 0;
}
}
}
[/AS]
Atleast thats what I thought would work. but the stupid thingie rotates to 108 degrees, then rotates back the other way BUT DOESNT STOP AT 72 DGREES!!!

what am I doing wrong?

Nasier