The retirement board shall maintain an individual account with each member, showing the amount of the member's contributions and the interest accumulations thereon. It shall collect and keep in convenient form data as may be necessary for the preparation of the required mortality and service tables, and for the compilation of such other information as may be needed for the actuarial valuation of the funds created by this article. The retirement board shall specify and adopt all actuarial assumptions for the system at its first meeting of every calendar year or as soon thereafter as may be practicable, which assumptions shall become part of the terms of the system.