The minimum unmodified allowance for service retirement under the Defined Benefit Program, exclusive of annuities payable from accumulated annuity deposit contributions and exclusive of the balance of credits in the member’s Defined Benefit Supplement account, shall not be less than ten dollars ($10) per month multiplied by the member’s years of credited service. This guaranteed amount shall be reduced by the amount of an unmodified allowance payable from a local system based on service credited under the Defined Benefit Program. If the retirement is effective at less than normal retirement age this allowance shall be reduced by one-half of 1 percent for each full month or fraction of a month that will elapse until the member would have reached normal retirement
age.