Note that the largest cost components for an aluminum smelter are electric-ity and the cost of alumina; together, they represent about 60 percent of total production costs. Because electricity, alumina, and other raw materials are used in direct proportion to the amount of aluminum produced, they represent per-ton production costs that are constant with respect to the level of output. The costs of labor, maintenance, and freight are also proportional to the level of output, but only when the plant operates two shifts per day. To increase output above 600 tons per day, a third shift would be necessary and would result in a 50-percent increase in the per-ton costs of labor, maintenance, and freight.