Simple inventory models assume that receipt of an order is instantaneous. In other words, they assume (1) that a firm will place an order when the inventory level for that particular item reaches zero and (2) that it will receive the ordered items immediately. However, the time between placement and receipt of an order, called lead time, can be as short as a few hours or as long as months (Heizer \& Render, 2014: 524). With this background, illustrate the reorder point graph and thereafter explain how the variables function in inventory management