The board shall by its rules provide for promotion in the classified civil service on the basis of ascertained merit and seniority in service and examination, and shall provide, in all cases where it is practicable, that vacancies shall be filled by promotion. All examinations for promotion shall be competitive among members of lower ranks who apply for the examination and who have the experience and qualifications required by the board as a prerequisite for taking the examination. The general manager of the Personnel Department shall submit to the appointing authority for each promotion the names of eligible applicants in accordance with Section 1010.
In rating eligible candidates, the board shall make an allowance of credits for past service. The announcement of the examination shall state that credits will be given for past service. Upon the written request of the appointing authority, the board may certify the names of those applicants having the highest ratings on the open competitive eligible list whose scores before adjustment for preferential credits are higher than the score of the highest available applicant on the promotional eligible register after credits for past service have been added. Names of candidates shall be removed from the register of eligibles for promotion after they have remained on the register for two years without re-examination.
Promotional examinations shall be held at intervals necessary to maintain a register of eligibles for promotional positions in which there are vacancies. The method and rules governing examination and certification for promotions shall be the same as provided for applicants for original appointment, except as otherwise provided in this section.