The Civil Service Commission shall provide for promotion to all positions in the classified service based upon competitive examination. Examinations may include written tests, oral tests and/or assessments centers or an evaluation of training and experience a credit allowance for seniority as established by Commission rule. Promotions will be made from one of the three highest standing persons on the Eligibility List certified by the Commission. Promotional exams may be restricted to present employees, or if recommended by the Manager, they may be opened to qualified candidates from outside the City service, by resolution of the Council.