Beginning July 1, 2013, and each year thereafter, this section shall govern annual actuarial valuations of the School Retirement Fund. In order to determine the additional required deposits by the State of Nebraska, as required by section 79-966, the board shall cause an annual actuarial valuation to be performed that will value the plan assets for the year and ascertain the contributions required for such fiscal year. The actuary for the board shall perform the annual valuation using the entry age actuarial cost method. Under this method, the actuarially required funding rate is equal to the normal cost rate, plus the contribution rate necessary to amortize the unfunded actuarial accrued liability on a level percentage of salary basis. The normal cost under this method shall be determined for each individual member on a level percentage of salary basis. The normal cost amount is then summed for all members. Beginning July 1, 2006, any existing unfunded liabilities shall be reinitialized and amortized over a thirty-year period, and during each subsequent actuarial valuation, changes in the funded actuarial accrued liability due to changes in benefits, actuarial assumptions, the asset valuation method, or actuarial gains or losses shall be measured and amortized over a thirty-year period beginning on the valuation date of such change. If the unfunded actuarial accrued liability under the entry age actuarial cost method is zero or less than zero on an actuarial valuation date, then all prior unfunded actuarial accrued liabilities shall be considered fully funded and the unfunded actuarial accrued liability shall be reinitialized and amortized over a thirty-year period as of the actuarial valuation date. If the actuarially required contribution rate exceeds the rate of all contributions required pursuant to the School Employees Retirement Act, the actuary shall determine the added contributions required to be paid by the State of Nebraska that constitute the difference between the actuarially required contribution rate and the rate of all other required contributions.