Denver Materials Company operates a recycling center that separates metals and then sells Objs. 2, 3 them to steel mills. The company uses large machinery to sort, move, and crush the metals. Denver's business throughout the year is uneven, in large part because the collection of recyclable materials varies greatly from month to month. In some months, the plant is slow. In others, supervisors have to authorize overtime to work the mountains of materials that the company receives. Management charges overhead costs to each job based on total machine hours for each batch processed. Explain how changes in volume and activity can distort the cost of each batch.