Additional calculated column after dynamic crosstab

[sunily]

Hi,

I have created a report based on user requirement to show list of (lets say) sales from last 13 months for each product. I created crosstab, product on rows and month on columns. Here is the complication. User also want to see the difference between first and last month values eg Feb 17 and Feb18 in a new column in same page.

I created a new data item to but I cannot append it next to crosstab like I generally add data items in list but it throw error "This object can only be inserted into a data container"

[sdf]

generally should work when you drag that in the side of the crosstab, make sure it is still in the inside and not outside the cross tab.
or better yet, add a crosstab space from the toolbar drag that in the crosstab and drag your new item there