Cumulative Totals

Is there a way to track running totals?   For example, we track the number of  days changed by change order.   This is then used to calculate the revised end date of the contract.  We track the completion date on our Contract Schedule of Values BP.   We enter the number manually as it changes.  I can create a query tab and a summary element that gives me the number of days changed,  but can't use the summary element in a formula.   This is clunky and unreliable.  The Summary Element would be perfect if it could be used in a formula.