The total statement performs two different operations. It calculates the changes that occur in a field or expression, and it also accumulates those changes into another field. There is a delta function that calculates only the changes that occur in a field or expression. This value can then be used as part of a larger expression. The total statement function used in the example above is equivalent to the following calculation:
This calculation takes the changes to the amount field and then adds that to the current field.