(1) Service credit for all covered employment with each employer will be credited to a retirement system on a cumulative basis for all purposes, including but not limited to calculation of benefits and application of any maximum hour restrictions, limitations, or requirements. A member may not be credited with more than full-time service credit as a result of this cumulation of service credit. Subject to the provisions of chapters 3, 5 through 9, and 13, a member must receive 1 month of service credit for each full month of service under rules adopted by the board.
(2) Service credits must be used in calculating a retirement or survivorship benefit.
(3) A retired member is not eligible to earn service credit.