SEC. 41. Inventories. - whenever in the judgment of the Commissioner, the use of inventories is necessary in order to determine clearly the income of any taxpayer, inventories shall be taken by such taxpayer upon such basis as the Secretary of Finance, upon recommendation of the Commissioner, may, by rules and regulations, prescribe as conforming as nearly as may be to the best accounting practice in the trade or business and as most clearly reflecting the income.
If a taxpayer, after having complied with the terms and a conditions prescribed by the Commissioner, uses a particular method of valuing its inventory for any taxable year, then such method shall be used in all subsequent taxable years unless:
(i) With the approval of the Commissioner, a change to a different method is authorized; or
(ii) The Commissioner finds that the nature of the stock on hand (e.g., its scarcity, liquidity, marketability and price movements) is such that inventory gains should be considered realized for tax purposes and, therefore, it is necessary to modify the valuation method for purposes of ascertaining the income, profits, or loss in a more realistic manner: Provided, however, That the Commissioner shall not exercise his authority to require a change in inventory method more often than once every three (3) years: Provided, further, That any change in an inventory valuation method must be subject to approval by the Secretary of Finance.