Thanks.
I have looked into GD::Graph, but as I have used it to get output you generate an image from it.
Now, I will be needing to regenerate this imagefile at least 10 times per second and I am in doubt as to whether perl can generate images at that rate.
Also the user should be able to watch the image as the graph is drawn. There are a number of javascript libraries for this (most notably maybe Google::Charts) but alas the users will have no access to the internet. There are other javascript opitons as well which abandoned for reasons I don't recall at the moment :).