I have 3 rows: new customer ; returning customer and purchases: every month the new customer is a different number, however I want the returning customer to add up for 36 months.
1st month: new customer+returning customer - which is 0
2nd month: new customer+returning customer of month 1
3rd month: new customer +r customer of month 1+2
4th month: new customer+ rcustomer of month 1+2+3
.....
36th month: new customer + rcusotmer of all months added up
here is a link how it looks like : http://s27.postimg.org/q4mt1vahf/Untitled.png
is there a formula by which i dont have to add up all separately? thanks!!!
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