Charting basic calculations

[Matthew R White]

I'm trying to make a simple chart that on the y axis displays the different months of the year, and on the x axis displays a numbers field in my database called Total Gross Commission. I've figured out how to attach (specify) the Total Gross Commission field on the x axis, however I cannot figure out the calculations bit on the y axis. Please help! :)

[comment]

A description of how your data is organized would help.