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Mike Hanson and Mark Goldberg continued with a previous project - a general purpose progress bar. Lots of nice techie code in there. I missed the first part (or parts) so I'm a bit adrift as far as how this class actually works.
One snag - there are potential problems with having a window definition stored with the class. If you attempt to open two instances of the class you'll get a GPF because you can't open the exact same window instance twice. So Mike switched to requiring an Init method to set up references to an existing window (and he put the class's window definition in an include so it can still be used).