In general, every improvement's materials, design, and workmanship are collectively assigned a grade from a to E, which represents a numeric multiplier that may raise or lower an improvement's assessment. Deer Creek Developers, Ltd. v. Dep't of Local Gov't Fin., 769 N.E.2d 259, 265 (Ind. Tax Ct. 2002). The "C" grade is given to "moderately attractive buildings constructed with average quality materials and workmanship throughout." IND. ADMIN. CODE tit. 50, r. 2.1-4-3(f) (1992). When challenging grade, a taxpayer may either submit probative evidence showing : (1) that the grade given to its improvement by the State Board was improper or (2) what the proper grade for his improvement should have been. Deer Creek, 769 N.E.2d at 265-66.