How to display the difference between two graphical curve

[vinch999]

Hi all,

I display 2 curves (only one curve in the serie option, the two data come from the same expression) . I want to display only the difference between these 2 curves. I tried Aggregation function but it doesn't work.
How to do that?
In the worst case,  I'll do that directly on the database
Cheers,

Vinc

[vinch999]

No idea? ???