Steel Fabricating, Incorporated manufactures furniture at its plants in Akron, Greensboro, and Schenectady. The company prepares monthly income statements segmented by plant. These income statements are organized to disclose contribution margin, performance margin, and responsibility margin for each plant, in addition to operating income for the company as a whole. The Akron factory employs two quality control inspectors at an annual salary of $70,000 each. These salaries should be classified as: