Mathematical easing

I am using the following code:

onClipEvent(enterFrame) {
if (this._xscale < 100) {
scaletarget = 100;
scalespeed = scaletarget - this._xscale;
scalespeed = scalespeed /2
this._xscale += scalespeed;
this._yscale += scalespeed;

My question is:

Is the above code more or less the same as using Flash’s built in easing?

If so, where would I need to start in order to execute complex mathematical easing?

Have a look here