In the case of a manufacturing, merchandising or mining business, "gross income" means the total sales less the cost of goods sold, plus any income from investments and from incidental or outside operations or sources. In determining the gross income, subtractions should not be made for depreciation, depletion, selling expenses, losses or for items not ordinarily allowable in computing the cost of goods sold.
3.26 Ark. Code R. 51-404(a)(1)