Add calculated rows to table for waterfall chart

Hello All,
I need help to add calculated rows in a data table. I have table with three raw columns and one calculated column. 
Col1                     Col2         Col3             Col4
category1              x1              y1               x1-y1
category2             x2             y2               x2-y2
                               .                 .
catergory200      x200        y200          x200-y200

Now I need to add few more rows that are calculations from other rows (the calculations are complex with all operators +,/,* and %). Following five rows needs to be added. 

Col1                            Col2            Col3         Col4
CalcCategory1           calc21        calc31         calc21 - calc31        
CalcCategory2          calc22        calc32       calc22 - calc32
CalcCategory3          calc23        calc33       calc23 - calc33
CalcCategory4          calc24        calc34       calc24 - calc34
CalcCategory5          calc25        calc35        calc25 - calc35

The newly added rows (underlined above in Col4) will be used to generate waterfall chart. I understand that to create a waterfall chart, the categories axis should be in rows hence I need data in this format. 


1) Is this right approach to create waterfall chart from calculated values?

2) Can I add calcualted rows?

Please help me. New approach to solve this is welcomed. 



(1) Answer