Flash _alpha losing accuracy

Question

I have this piece of code:
this._alpha = Math.round(this._alpha + this.fadespeed);
trace("before:" + this._alpha);
this._alpha = Math.round(this._alpha);
trace("after: " + Math.round( this._alpha));
which is used within a hit test to fade in/out a MC when the
mouse hovers over it. For some reason though, even though _alpha
starts off as 0, and this.fadespeed = 5, and i have the Math.round
function there, i get:
before:4.6875
after: 5
before:9.765625
after: 10
before:14.84375
after: 15
before:19.921875
after: 20
before:25
Anyone know where im going blatantly wrong, or if i need to
do an explicit data type cast anywhere. The Math.round function is
returning the correct value, just the _alpha variable in the MC
doesnt want to hold integers it seems!!!
Im using Flash MX 2k4

Answer 1

> flash stores the _alpha property internally as an
integer between 0 and
> 255.
Actually .. it stores that value as an integer between 0 and
256; where 0 =
0% alpha and 256 = 100% alpha. That's why you can get
accurate results with
(say) 50% (which translates exactly to an internal value of
128.
I know why you might thing it should be 255 .. but its not :)
Other than that, your explanation was correct :)
Jeckyl