All bonds or other evidences of debt held by an admitted incorporated insurer if amply secured and if not in default as to principal or interest may, in the discretion of the commissioner, be valued as follows:

1. (a) If purchased at par, at the par value.
2. (b) 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 the effective rate of interest on the price at which the purchase was made.

3. (c) In such valuation, the purchase price shall in no case be taken at a higher figure than the actual market value at the time of purchase.

   The commissioner shall have full discretion in determining the method of calculating values according to the foregoing rule, the values found by him in accordance with such method being final and binding.