40 ILCS 5/5-133

"Widow's Prior Service Annuity" shall be credited for the widow of a male present employee for service prior to the effective date, in accordance with the "Policemen's Annuity and Benefit Fund Act of the Illinois Municipal Code" and this Article. The amounts so credited shall be improved by interest at 4% per annum during the employee's service subsequent to the effective date until he attains age 57.