Little bit more explanations : using a marker like this one, the bottom pointing on a location.
I make this action : onover="tween(scale,1.5);"
Works well, but scale origin is top center, so the bottom of the marker moves.
I would prefer scale origin to be bottom center, so the marker keeps pointing to the same place.
Sure it is very easy, but I can't find how 
Hope you can help !