(a) A participating member is immediately and fully vested in that member's contributions and related earnings.


(b) A member is fully vested in the employer contributions made on that member's behalf, and related earnings, after five years of service. A member is partially vested in the employer contributions made on that member's behalf, and the related earnings, in the ratio of


(1) 25 percent with two years of service;


(2) 50 percent with three years of service; and


(3) 75 percent with four years of service.