Subject to the above restrictions, and to such other rules and regulations as may be prescribed by the board, the board shall ascertain, as soon as practicable after said statement is filed, the amount of prior service, if any, to which each member is entitled and shall issue to such member a prior service certificate certifying the length of service rendered by him. Any period or periods during which any such member has been on leave from service, without compensation for service, shall not be counted in his prior service credit.
T.C.A. § 8-3419