A typical storage run usually computes charges for the period of time after the storage run occurs; i.e. into the future. If the Next Bill Date is 4/1/2008, for example, then a quarterly run will be computing charges for April, May, and June.
The Is Arrears flag can be set to instruct the application to compute charges based on the period of time prior to the storage run. If the Next Bill Date is 4/1/2008, then the quarterly run will include January, February, and March.
Figure 39: Is Arrears example for a quarterly billing run