How to Sum Distinct Values within Expression on a Chart

[#1]

Hi
I am creating a Chart, Lines with Bars. The lines are a sum of a column this is easy to do. But the bars need to be the sum of distinct values of certain column.
For example:
         

Header 1	Header 2	Header 3
4/1/2014	A.1	5
4/1/2014	A.1	5
4/1/2014	A.2	25
5/1/2014	A.3	30
5/1/2014	A.3	30
5/1/2014	A.3	30
5/1/2014	A.3	30

What I am trying to do is for each month in the chart the Bar will be the distinct sum of Header3. So lets say the user choose A.1 and A.2  from a list box for just April 2014, the distinct values of Header 3 are 5 + 25 = 30 and would be the value of the bar, I do not want 5 +5 + 25.

Any Ideas?

Thank You

[Anonymous · Accepted solution]

You can use "distinct" in sum:

sum(distinct Header3)

[#3]

Thank You it worked, awesome.