It is an inventory control method where orders are periodically placed, but the order quantity is different every time, and is also called Fixed Period Deficit Ordering System. The method has the following features: 

* An order is periodically placed.

* The order quantity is different every time.

* Even relatively large fluctuations in demand can be handled properly.

* Even seasonal variation can be handled modestly.

* The inventory volume can be reduced compared with ordering point system.

* A-group items are usually best for this method.

* Longer lead time is acceptable.

* Longer time for paperwork is needed.

Every order quantity in thier method is obtained by the following formula.