MACROMEDIA FLASH 8-LEARNING ACTIONSCRIPT 2.0 IN FLASH Manual page 718

If you add a local variable to the Watch list, its value appears only when Flash Player is
stopped at a line of ActionScript where that variable is in scope. All other variables appear
while the SWF file is playing. If the Debugger can't find the value of the variable, the value is
listed as undefined.
If necessary, you can resize the various regions of the Debugger panel. When your
changes between each region, you can drag to resize the Display list, Watch list, and
code view.
The Watch list can show only variables, not properties or functions.
Variables marked for the Watch list and variables in the Watch list
To add variables to the Watch list, do one of the following:
On the Variables or Locals tab, right-click (Windows) or Control-click (Macintosh) a
selected variable and then select Watch from the context menu. A blue dot appears next to
the variable.
On the Watch tab, right-click (Windows) or Control-click (Macintosh) and select Add
from the context menu. Double-click in the name column, and enter the target path to
the variable name in the field.
To remove variables from the Watch list:
On the Watch tab or the Variables tab, right-click (Windows) or Control-click
(Macintosh) and select Remove from the context menu.
718 Debugging Applications