Given a dialog with two grid-style tables, what's the best approach to visually showing that the selected row of the left table is what populates the right table? The best I can think of is an arrow between the tables, but the problem that is the divider between the tables is drag-able (tables re-size to fill the space they're given), so I feel like an arrow says "drag this way" or "collapse this side."
I've considered an arrow that always stays next to the selected row, but typically there will be many more rows than are visible, and it seems like calculating the placement of the arrow could be a bit of a pain.
Is there an obvious solution anyone else sees, or should I bite the bullet and go with the arrow?