Update a total

Update a total

I saw the expense chart application that keeps track of a total amount separate from a form where you enter a certain amount and then shows it in chart view. However, I want to be able to edit the running total if a certain record is updated.

Say, if I had a form expenses where uses can enter the data, another form keeps track of the total for each person. But if a person makes a mistake on the expenses form and decides to edit it, how could i change the total in the other form?