overlay graphics

how can I do to overlay two graphs having a point of overlap?

 the image below as an example:

http://imageshack.us/photo/my-images/252/overlaygraph.jpg/

observation: ponto de sobreposição mean point of the image overlay, this image is in Portuguese in Brazil.

Thanks in advance.

[Walter Roberson]

Interesting question.

Are there curves drawn on both parts, or just on one part?

[Artur M. G. Lourenço]

curve is not only in front of the chart, the chart that are behind the points are plotted in dispersion.

Answer 1

[Artur M. G. Lourenço]

someone?