aterial item. See Treas. Reg. § 1.481-1(a)(1); Graff Chevrolet Co. v. Campbell, 343 F.2d 568, 570-571 (5th Cir. 1965), Knight-Ridder 743 F2d at 798, Peoples Bank & Trust 415 F2d at 1344, Ryan v. Commissioner, 42 T.C. 386, 392 (1964). Once the Commissioner has imposed a change in accounting method, the application of IRC § 4