Section 13-641. Annuities; annuities to retired employees

Any person retired
  from  active  service  pursuant  to  sections  13-639 and 13-640 of this
  chapter, shall be awarded and granted by the board of estimate an annual
  sum or annuity to  be  fixed  by  such  board  not  exceeding,  however,
  one-half  of  the  amount which his or her annual salary or compensation
  averages for the period of three years immediately prior to the time  of
  his  or  her retirement. The comptroller shall pay the annuities granted
  in monthly installments.  Such  payments  are  to  continue  during  the
  lifetime  of  the  person or persons so retired. There shall be included
  annually in the budget such sums as may be required for such payments.