UW

I'm not familiar with InvalidateRect API, but if I understand you properly,
you only issue this when you need to refresh the PictureBox (ie, if datapoint
is beyond current graph extremes).

If this is correct, do you by any chance know in advance what the min and/or
max values of x and y will be? If so, perhaps as a test, you could simply
omit the "zoom to fit" feature.. just see if you can populate the graph with
all pieces of data. If that works, we can move on to the "next step."

Spoo