"Stack Series" chart in open office calc
 

Hi all,
I hope i'm posting this in the right forum. I'm trying to create a line chart using open office calc 3.0.1. What I'm after is a cumulative chart (ie each value along the x axis includes all previous values). When choosing the chart type, the "Stack Series" option is available, however, enabling this doesn't have any visible effect.

Google, the open office wiki and a search of these forums hasn't turned up any results. Any ideas?

Thanks.