I am trying to figure out a way to reset the cumulative sum every time I reach $600.
For example my customer pays me random sums every month, as soon as the total amount reaches 600, I would like to reset the counter and start counting the amount from $0 until the next cumulative sum of $600. If by month 6, my customer has paid $650, then I'd like to carry over the $50 to the next set of cumulative sum.



