chart web part: how to display list items across time?

Hi,

I have a list, which holds the job applications we receive through our website. A column indicates whether the application is spontaneous, or whether it relates to an open position.

I'd like to display in a graph the number of applications received per week, for both types of applications. So my X axis would be the week number. I already added a calculated column to my list, which holds the week number (based on the Created column). My Y axis would be the sum of applications received per week.

How can I implement this with the chart web part? I successfully put my calculated column as X axis, but how do I get the sum of application in Y axis? And how can I have my two series of values (spontaneous and job applications) next to each other?

Any advice is welcome.

Thanks,

Pierre