Each person appointed to membership on any county board of equalization shall, before entering upon the duties of such office, take and subscribe to the following oath, in addition to the oath required of regularly elected state and county officials: "I do solemnly swear that I will faithfully discharge the duties imposed upon me by law as a member of the county board of equalization, and that I will adjust, equalize, and fix the taxable value of all property listed for taxation and submitted for review to the board of which I am a member on a basis of its fair and reasonable market value to the best of my knowledge and ability, so help me God." Said oath, together with the other official oath required of such board member shall be filed for record in the office of the judge of probate of the county in which such board member is to serve.