(1) The property factor of the apportionment formula for each trade or business of the taxpayer shall include all real and tangible personal property owned or rented and used during the tax period in the regular course of such trade or business.

(2) Property used in connection with the production of non-business income shall be excluded from the property factor.

(3) Property used both in the regular course of taxpayer's trade or business and in the production of non-business income shall be included in the factor only to the extent the property is used in the regular course of taxpayer's trade or business. The method of determining that portion of the value to be included in the factor will depend on the facts of each case.

(4) The property factor shall reflect the average value of property includable in the factor as set forth in ARM 42.26.237.