BEE-UUU-TEE-FUL! That's it.

Jon,
Thanks for the link to your workbook or I don't think I would have
been able to decipher the staggered data in the forum message. I
appreciate your efforts in providing such a detailed explanation. I
can see that I need to read more about how Excel handles dates, since
in the examples I've seen, dates were handled as categories not as
discrete values. When I developed my curve I converted date to
decimals to get "values" (Aug 1875 became 1875.66). It looks like I
didn't have to do this.

On first looking at your area series cell entries, I was puzzled.
Fortunately, you used the wierd serial numbers 533 and 567, which
revealed most of the entries are differences. Then I realized that,
with a stacked chart, the difference increment is what has to be added
to the stack to get to the required serial number for the horizontal
line defining the top of the specific area.

I should be able to add cell references, and the difference function
where applicable, to the table of specific area cell values that refer
back to the cells of the "cumulative" curve. Then, if I should tweak
the curve, the areas will automatically update and resize.

I also learned something from the way you handled the cumulative
curve. I used separate series for each segment to avoid getting a
vertical black line at the ends of the blank areas. But now I have to
format each series separately. You elegantly handled all three series
as a unit with blank cells to remove the undesired line segments. Now,
any format change will affect all the series at once. Nifty!

Thanks again for being so generous with your time and knowledge.
Paul