How to show negative value in Pie Chart from Webi?

I have below example data, I want to convert this to a pie chart in Web Intelligence, my problem is after I convert it to a pie chart, the revenue '-30' is shown as '30', looks like the pie chart is not suppor the negative value to show, I want to know if there is any workaround or solution to make the pie chart to show the negative value? Is this behavior is by design? do we have any official document to explain this?

The product I used is BOE XI 3.1 SP3.

Department Revenue

A 100

B -30

C 80

Edited by: Alex Wang on Jul 13, 2010 5:51 PM