Negative values

This plug-in is just what I have been looking for. A question though.
I am trying to display some simple financial data. It requires a bar chart with some positive and some negative values. I’d want the positive bar values to ascend from 0 and the negative values descend from the 0 (x-axis) line. Any way to do this?
I’m also getting somewhat frustrated with the detailed Y-axis scale. I’d appreciate any help.
http://www.brfingemar13.se/en/dokument/arsrapporter/

Thank you so much for this great plugin.

http://wordpress.org/extend/plugins/wp-charts/