How can I perform calculations on multiple baserows in my horizontally

[ncalcaterra]

Here's my tiny example... I have a report with a column definition that includes a column for calculating the % of Gross Sales as well as a column for calculating the % of Net Sales. In the Row Definition, I set the CBR to row 280 (gross sales). A little further down in the rows I set the CBR to row 340 (net sales).

Heres what I don't understand 'how' to do... If my columns are obviously going horizontally across the page and one column wants to calculate the percentage off row 280 (gross sales), but the next column wants to calculate the percentage off row 340 (net sales), 'how', when using 'baserow' in your column definition does it know 'which' baserow to calculate from? If this report was vertical, I could understand how there can be multiple baserows. But how, in a horizontal layout, can I have multiple baserows to calculate from?

I hope I made sense! Thanks for any help you can provide