Lets says that below are my monthly incomes and spendings.
I want to figure out what is the number when I am most negative and most positive during the month. Using excel of course.

Data:
+$120
-$90
+$20
+$100
-$80
-$60
-$60
+$110
SUM: +$10

Explanation by hand.
If you were to sum these up by hand, at the end of the month, I would be +$10 , but during that month, I would have been -$50 and +$150 as my most negative and most positive holdings respectively.