English: Diagram depicting economies and diseconomies of scale. A firm can grow or shrink in size, in the long run, i.e. in the diagram, can move up and down the Long Run Average Cost Curve. The Long Run Average Cost (LRAC) curve plots the average cost of producing the lowest cost method. The Long Run Marginal Cost (LRMC) is the change in total cost attributable to a change in the output of one unit after the plant size has been adjusted to produce that rate of output at minimum LRAC. As a result, the Long Run Marginal Cost (LRMC) is the change in the total of cost of adding one more unit when the long run costs are at a minimum.