in reply to Real time data graphs.
Just an idea for an alternate way to go about it. Consider having Tk::Canvas only show a finite time period, say the last hour for example, Continue to save the data points in an array, and at program completion use Image::Magick or some similar graphics generating package generate a graph containing the full graph.
Not certain if it would work for your particular task, just figured I'd offer another potential way to attack the problem, and it might help solve the problem RobPayne mentioned of only a limited amount of space to draw in.
Just Another Perl Alchemist