The bullwhip effect is a visual description of the transmission of demand information distortions in the supply chain. To put is in a simple way, the forecasted customer demand is 10 units, and when it comes to the retailer orders, it becomes 15 units including the safety stock. Then the distributor ordered 20 units in order to get the bulk discount and keep stable stock, then the manufacturer finally produced 40 units to bring down the manufacturer cost. But the actual quantity the customer needed is 9 units, this is so-called bullwhip effect.