How to use the "field to group" for multi-series on the same graph?

Hello, it's my first post on Drupal.org, and excuse my for my english :)
My request is: How to use the "field to group" for multi-series (specially Line, Area, ...) on the same graph?
I explain, if we have something like that:
Field1 | Date VL | VL
-------------------------------------
F1 | 07/12/2007 | 165,91
F2 | 07/12/2007 | 354,96
F1 | 14/12/2007 | 178,34
F2 | 14/12/2007 | 356,01
F1 | 24/12/2007 | 159,37
F2 | 24/12/2007 | 358,88
F1 | 28/12/2007 | 122,85
F2 | 28/12/2007 | 363,37
Chart setting:
-Fields to be used in Chart Series = VL
-Fields to be used as X axis labels = Date VL
I'm using field1 as a field to group and i get 2 graphs, but i want get one graph with 2 Line (one for each value of Field1)

N.B:
-We must choose the intersections for the X axis if the values are different (but intersections are guaranteed)
-Ability to use the "Field to group" values as label for Chart Series.
-Ability to scale the values of the graphs if they are very distant (scaling formula VL(to represent)= VL(i)/VL(b)*100; VLb=Reference VL: the first for exemple )

Thank you for your attention
Abdel