You probably want the slide to update while the while loop in the subVI is running, so you can't simply wire an output from the subVI to the main VI. So you are going to have to use some form of communication between the two VI's other than a hard wire. For this simple case I think I would recommend using a global variable. You could also use DataSocket or even write the value to disk, but using a global is probably the easiest method for this case. I've attached your modified VI's. Let me know if this works for you.
Robert Mortensen Software Engineer National Instruments