(2) The commission shall establish maximum and minimum salary limits for each grade in its classification, and shall provide by rule for advancement or promotion from grade to grade on the basis of efficiency and length of service.
(3) The classifications and grades may, from time to time, be amended, added to, consolidated or abolished by the commission, but no person holding any position under any established classification or grade shall be affected by any such change so as to deprive the person of any of the benefits attached to the classification or grade applicable to the position then held by the person.
(4) The positions so classified and graded shall constitute the classified civil service of the county.