Using generic load data in a chart

[dafnis14]

Dear All,

Based on other posts, I have created a generic load in order to create a table with sales for   events taking place on  different dates  in consecutive years.  Each column represent a day of the event.

The document includes a straight table with the desired data.

My challenge is to have  calculations such as  the difference in sales  in each column. So what is the best way to do it?

Thanks! !