In constrast, IMP considers both traditional input and non-traditional input (quality and flexibility). The latter enables managers to trace the output beyond production. For example, decreasing inventory cost (a flexibility cost element) indicates a sales increase because the inventory is the difference between production and sales; if the inventory cost is zero, it means that all the products are sold. Further, decreasing external failure cost (a quality cost element) signals decreasing returns of sold products, that is, increased customer satisfaction. Since the IMP ratio traces products all the way through production, sales and even returns, it can evaluate whether or not the company makes money through customer satisfaction, that is, 'manufacturing effectiveness'.