In Duval Sierrita Corp. v. Arizona Department of Revenue, 116 Ariz. 200, 203, 568 P.2d 1098, 1101 (App. 1977) the Court examined whether machine parts were "used directly in . . . metallurgical operations" under A.R.S. 42-1409(B), a tax exemption statute (The statute is now codified at A.R.S. 42-5159). To determine whether conveyor belts, booster pumps and steel pipes were "used directly," we looked to their ultimate function, and the Court determined that they made the mining and metallurgical operation an "integrated system." Id. at 205-07, 568 P.2d at 1103-05. Wary of drawing "arbitrary lines," the Court found that those disputed parts qualified for the exemption. Id.