In any county or district, subject to Section 31676.12, which adopts or has already adopted the provisions of this article, the retirement allowance of members subject to Section 31676.12 shall be computed according to either the provisions of subdivision (a) or subdivision (b) of this section as selected by the board of supervisors.

(a) The retirement allowance for service rendered prior to the effective date of this article as specified in the resolution mentioned in Section 31800 shall be computed in accordance with the provisions of Section 31676.12. The retirement allowance of any member with respect to service performed after the effective date of this article as specified in the resolution mentioned in Section 31800 shall equal the total of the following:

(1) The fraction of one seventy-fifth of the first three hundred fifty dollars ($350) monthly of the member’s final compensation set forth in the table appearing in Section 31676.12 in the column applicable to his age at retirement taken to the preceding completed quarter year multiplied by the number of years of creditable service as provided therein.

(2) The fraction of one-fiftieth of any remaining portion of the member’s final compensation set forth in the table appearing in Section 31676.12 in the column applicable to his age at retirement taken to the preceding completed quarter year multiplied by the number of years of creditable service, or

(b) The retirement allowance shall be computed according to the provisions of Section 31676.12 and federal old age and survivors’ insurance coverage shall be on an additive or supplemental basis.

(Amended by Stats. 1973, Ch. 55.)