I don't understand Local To Global

In this program the rocks(and the bases on them) move around a centrally located ship.
The rocks and ship are children of the playscreen and the bases are children of the baseHolder
which is a child of the playScreen . In the parent of playScreen (view) i want to trace out
the x and y coords of the ship and the 1st base (added to an array called baseArray at [0].

trace("Global ship coords :" + playScreen.localToGlobal(new Point(playScreen.ship.x, playScreen.ship.y)));
trace("Global AsBase coords :" + playScreen.localToGlobal(new Point(playScreen.baseArray[0].x, playScreen.baseArray[0].y)));

This is my current code and it gives me values but these values don’t change as they all move around the screen.
This of course leads me to my title “I don’t understand LocalToGlobal”.
Can anyone shed some light???