The idea is to show only the last n minute period of aquisition and n should be configurable by the user. With the resources available now, the best way to do this seems to be by working with as many Tk points as there are horizontal pixels in the graph and make a transformation on the data so that the data points are represented by Tk points.
But this is makes things unnecessarily complex. The best would be to be able to use imager primitives directly on a canvas, in some way.