7-3-1250. Compensation of officers and employees. The compensation of officers and employees in the administrative service of the municipality shall be fixed by ordinance, but all positions in such service, except those of heads of departments and heads of offices not included within regular departments, shall, for purposes of compensation, be graded and classified by the manager according to duties and responsibilities. The commission shall by ordinance establish a schedule of compensation for the positions so graded and classified, which shall prescribe uniform compensation for like service as determined by the grading and classification by the manager. Such schedule of compensation may establish a minimum and maximum for any grade, and an increase in compensation within the limits provided for any grade may be granted by the manager upon the basis of efficiency and seniority.