(1) Property owned by the taxpayer shall be valued at its original cost.   As a general rule "original cost" is deemed to be the basis of the property for federal income tax purposes (prior to any federal adjustments) at the time of acquisition by the taxpayer and adjusted by subsequent capital additions or improvements thereto and partial disposition thereof, by reason of sale, exchange, abandonment, etc.

(2) If the original cost of property is unascertainable, the property is included in the factor at its fair market value as of the date of acquisition by the taxpayer.

(3) Inventory of stock of goods shall be included in the factor in accordance with the valuation method used for federal income tax purposes.

(4) Property acquired by gift or inheritance shall be included in the factor as its basis for determining depreciation for federal income tax purposes.