Cumulative Value of KPI

Dear community,

is there a way to display the running sum of a certain KPI? We want to calculate our cumulative savings generated through the reduction of price changes but I can only get the value for a certain point in time (Formula:
(KPI(“Count Items”) * 0.15 - KPI(“Count Items”) * KPI (“Price Change Rate”)), yet not for a running value . I tried this SUM (KPI(“Count Items”) * 0.15 - KPI(“Count Items”) * KPI (“Price Change Rate”)) but I get an error message.

Any help would be appreciated.

Best regards,

Carl