(a) All bonds or other evidences of debt having a fixed term and rate of interest held by any insurer may, if amply secured and not in default as to principal or interest, be valued as follows:

(1) If purchased at par, at the par value.

(2) If purchased above or below par, on the basis of the purchase price adjusted so as to bring the value to par at maturity and so as to yield in the meantime the effective rate of interest at which the purchase was made, or in lieu of such method, according to such accepted method of valuation as is approved by the commissioner.

(3) Purchase price shall in no case be taken at a higher figure than the actual market value at the time of purchase, plus actual brokerage, transfer, postage or express charges paid in the acquisition of such securities.

(4) Unless otherwise provided by valuation established or approved by the commissioner, no such security shall be carried at above the call price for the entire issue during any period within which the security may be so called.

(b) The commissioner shall have full discretion in determining the method of calculating values according to the rules set forth in this section: Provided, That no such method or valuation shall be inconsistent with any applicable valuation or method used by insurers in general or any such method then currently formulated or approved by the committee on valuation of securities of the national association of Insurance Commissioners or its successor organization.