The actuary appointed by the commission shall recommend and the board shall keep in convenient form, such data as shall be necessary for actuarial valuation of the fund every year. Once in every 3-year period the actuary shall make an actuarial investigation into the mortality, service and compensation or salary experience of the members and beneficiaries of the fund and shall make a valuation of the assets and liabilities of the fund. Upon the basis of such investigation and valuation the commission shall:
For the purpose of the valuation the commission shall classify the members in such group or groups as it deems necessary.
N.J.S. § 43:10-18.17a