Area Charts With Negative Numbers

[Ritujoy]

I'm curious if anyone has had success trying to design an area chart
as described below:

1) The graph depicts annual benchmarks / net returns (Y-AXIS) versus
year (X-AXIS).

2) I have three arrays for benchmarks. Array 1 is the bottom quartile,
array 2 is the median and array 3 is the top quartile. If you picture
the entire graph, these three arrays break up the chart into four
regions. Everything below array 1 is the bottom quartile. Everything
between array 1 and array 2 is the 3rd quartile. Everything between
array 2 and array 3 is the 2nd quartile and everything above array 3
is the top quartile.

3) Currently I'm generating line plots for all the arrays.

4) I would instead like to have four "areas" on the chart each with
their own color. Using area charts doesn't seem to work because it's
looking for absolute value changes.

(5) My crude work around was to set a max, min and scale for two
charts and then shift one chart to be all positive (add 100% to all
the array values). Then I put the shifted graph below another graph
with the real axis (but same scale).

Has anyone thought of a more elegant way or alternatively know how to
use Excel to accomplish this?

 

[Ritujoy]

Thanks to Andy Pope for developing a solution. The correct method is
to shift all the benchmark points to be non-negative and then plot
these new series on a secondary axis. Simple - should have seen it.

Thanks,

Ryan