Multiple items selected in a listbox

[#1]

Here is my scenario:

Product ListBox

          A

          B

          C

          D

What I would like to show in a Bar Chart are the following:

1.  If a person selects on Product, lets say A, a bar graph of how many they have.  This is easy.

2.  If a person selects 2 Products, lets say A and B, a bar graph that shows the total number of A and the total number of B only if A exists. 

So basically the second product selected depends on the first product selected.

Does this make sense?

David

[Gysbert_Wassenaar]

See attached example.