Plot the lower threshold line and the *difference* between the lower and
the upper thresholds. Move each of these series to the secondary axis,
change each to stacked area type of chart, add a secondary x axis (with
the chart selected, select Chart | Chart Options... | Axes tab | check
on the 'Secondary x axis'), format the secondary x-axis to *not* check
'Value (Y) axis crosses between categories', and format as desired.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
Multi-disciplinary business expertise
+ Technology skills
= Optimal solution to your business problem
Recipient Microsoft MVP award 2000-2005

In article , =?Utf-
8?B?Si5TLiBSeWJhaywgUC5Fbmcu?= <J.S. Rybak, P.Eng.
@discussions.microsoft.com says...
I want to shade the area between 2 line plots i.e maximum curve and minimum
curve. Everything in between the two lines is valid. thus the area needs to
be shaded to create an envelop effect.

anyone ever done this before