It's traditional--perhaps dysfunctionally so--for Tk-ers to code
their own progressbars, often on the model found in the
"[Bag of Tk algorithms]".  It's certainly true that Tk makes it
easy.  [mkWidgets] and [BWidgets] build in progressbar widgets.
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Also a nice and simple progress bar is the one by DKF at:
http://www.cs.man.ac.uk/~fellowsd/tcl/mwidx.html#progress
It is also able to display the percentage along with the
filled rectangular...

George




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Practical development of progressbars often involves questions of how to
"[keep a GUI alive during a long calculation]".