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The maker, Scott E. Thile, is a piano tuner and musician who began carving pipes in 2006. Until August 2012 he used an ascending grade scale of D, C, B, and A, after which grading was discontinued. The two-digit number in the stamp gives the year of production (07 = 2007), and the number following it gives the production sequence; in 2013 the Etude (ET), Opus (OP), and Freehand (FH) lines were introduced.