Before meeting to assess the damages for the taking, all commissioners shall qualify by filing with the sheriff a written oath that they will to the best of their ability faithfully and impartially assess damages and make a written report assessing the damages to the sheriff. [C24, 27, 31, 35, 39, § 7828; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §472.7 ] C93, §6B.7 99 Acts, ch 171, §8, 42 ; 2000 Acts, ch 1179, §14, 30