Sec. 5.11. 13TH CHECK FOR RETIREES. (a) In any fiscal year ending after 1996 for which the board determines that the average annual investment yield on the market value of fund investments for the preceding five fiscal years exceeded the annual investment yield projected by the actuary for that preceding five-fiscal-year period by at least 100 basis points, the board may authorize the disbursement of a 13th pension check.

(b) The 13th pension check is paid to each retiree who is entitled to receive an annuity in the last month of the fiscal year preceding the fiscal year in which the check is disbursed and is in an amount equal to the amount of the annuity payment made in the last month of the preceding fiscal year, except the amount of any such check shall be prorated for any retiree who has been receiving an annuity for less than one year so that the amount of the check is one-twelfth of the check that would have been paid to the retiree receiving an annuity for a full year times the number of full months an annuity has been paid.

(c) Authorization of a 13th check for any year is subject to the discretion of the board. Authorization for one year does not obligate the board to authorize a 13th check for any other year. The 13th check shall be paid as the board directs.

(d) In this section, "annual investment yield" means the yield on the fund's investment portfolio for a particular year, as a percentage of the portfolio, after reduction for costs of investing the portfolio, but without reduction for the fund's operating expenses.