Effective July 1, 1970, and each succeeding July 1, the total monthly service or disability retirement allowance rate paid for the month of June, 1969, to any member retired prior to July 1, 1969, shall be increased by one and one-half per cent (1 ½%) of such monthly allowance rate for each year that the member has been retired, but the aggregate of such monthly increments to any retired member's allowance shall not exceed thirty per cent (30%) of his June, 1969, monthly service retirement allowance rate if he retired prior to July 1, 1969.
T.C.A. § 49-1561