In the example below, I've created the Actuals list but need help with the Cumulative List creation which as part of the running totals needs values from the Actuals List. I believe I'll need to use "previous" value in conjunction with group by in order to get running totals for each month but I am not sure how to syntax this. 

Actuals List

Month         Count
Oct                  1
Nov                 2
Dec                 2
Jan                  3
etc..

Cumulative List

Month          Count
Oct                 1 (Oct Actuals)
Nov                3 (Cum Oct + Actuals Nov)
Dec                5 (Cum Nov + Actuals Dec)
Jan                8 (Cum Dec + Actuals Jan)

Thank you for your help in advance!