t is 10 percent, leaves us with the `definite and firm conviction that a mistake has been made.'" 1-1}No. 13-60472 (September IS. 2014) overturning Estate of Elkins 140 T.C. No. 5 (March I I, 2013) :Mr. Hall is a Managing Director of FMV Opinions, Inc.. a national valuation and investment banking firm with offices i