HP 39gs Master Manual page 88

Nice table values
What makes this view even more useful is that the table keeps its 'nice'
scale even while the usual tools are being used. As you can see
in the screenshot left, the table is automatically repositioned to show the
closest pixel value to that of the extremum found.
The Signed Area tool is also available in this view and when the cursor
is moved the values in the table follow it. Unfortunately, the highlighted value in the table doesn't change as
the cursor moves to create the shaded area. For this reason the best strategy is to use the key to jump
to the end point. This means that the area will not be shaded but this should not be a problem.
Overlay Plot
Another possibility from the menu is Overlay Plot. This option can be used to add another graph
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over the top of an existing one, without the screen being blanked first as it usually is. As an example, if you
have already graphed functions through to and then add another one in the view, then
F1(X) F6(X) SYMB
you may not want to have to wait while all the earlier ones are redrawn. If you un- the earlier graphs
and then use Overlay Plot for the new one then it will be drawn over the top of the existing ones. Of course
the results will not be good if the scales don't match!.
More usefully, you can use this to combine different styles of graphs. For
example, the screen shot right was produced by drawing a circle in the
Parametric aplet and then superimposing the equations y = x and y = -x
in the Function aplet. This could be used to show, for example, the
enclosing curves for conic sections.
You can also use this technique to overlay functions on top of statistical graphs. Again, the important point
would be to ensure that the scales matched.
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