Please notice the values in the fields. Click on "Preview Graph 1" & "Preview Graph 2" to see the graphs with the current field values. Now change the values and preview the results again. You'll notice the graph changing to match the new values.
The popup windows are "graph1.php" and "graph2.php". If you were to put these into your browser with no data behind them, they will only show the shell of the graphs with no data.