2 TweenMax scaling questions.

When the symbol scales it scales from the top left .

1) How do you have it scale from the center so that it seems to grow from the middle and not the far top left?

2) Using AS2 and TweenMax, I can't seem to make rhyme or reason from the use of the parameters _xscale and _yscale..what is the method of measurement ? When I use _xscale=100 it makes it huge. When I use 10 it makes it real small.
What I am trying to to do is make the effect of it pop up from a smaller (2/3 size of it's size o it's full size which is 75x75 with an elastic bounce .

Thanks in advance.

TweenMax.to(this["SQ" + ll], 5, {_xscale:75, _yscale:75, ease:Elastic.easeOut});