The legislature provided significant guidance for the determination of whether costs incurred by a coal producer are direct or indirect mining costs when it enacted Wyo. Stat. Ann. 39-2-209(d) (Michie 1997) (repealed & recreated at 39-14-103(b)(vii)(A-D) & 39-14-101(a)(viii) in 1998). Under this statute, which applied to all mineral production on or after January 1, 1990, the terms "direct costs" and "indirect costs" were specifically defined. Before its repeal and recreation in 1998, 39-2-209(d) provided in pertinent part: (d) for coal sold away from the mouth of the mine pursuant to a bona fide arms-length sale, the department shall calculate the fair cash market value of coal by multiplying the sales value of extracted coal, less transportation to market provided by a third party to the extent included in sales value, all royalties, ad valorem production taxes, severance taxes, black lung excise taxes and abandoned mine lands fees, by the ratio of direct mining costs to total direct costs. Nonexempt royalties, ad valorem production taxes, severance taxes, black lung excise taxes and abandoned mine lands fees shall then be added to determine fair market value. for purposes of this subsection: (ii) Direct mining costs include mining labor including mine foremen and supervisory personnel whose primary responsibility is extraction of coal, supplies used for mining, mining equipment depreciation, fuel, power and other utilities used for mining, maintenance of mining equipment, coal transportation from the point of severance to the mouth of the mine, and any other direct costs incurred prior to the mouth of the mine that are specifically attributable to the mining operation; (iii) Total direct costs include direct mining costs determined under paragraph (ii) of this subsection plus mineral processing labor including plant foremen and supervisory personnel whose primary responsibility is processing coal, supplies used for processing, processing plant and equipment depreciation, fuel, power and other utilities used for processing, maintenance of processing equipment, coal transportation from the mouth of the mine to the point of shipment, coal transportation to market to the extent included in the price and provided by the producer, and any other direct costs incurred that are specifically attributable to the mining, processing or transportation of coal up to the point of loading for shipment to market; (iv) Indirect costs, royalties, ad valorem production taxes, severance taxes, black lung excise taxes and abandoned mine lands fees shall not be included in the computation of the ratio set forth in this subsection. Indirect costs include but are not limited to allocations of corporate overhead, data processing costs, accounting, legal and clerical costs, and other general and administrative costs which cannot be specifically attributed to an operational function without allocation. This method attempted to value coal production at the "mouth of the mine" in order to establish the value of the coal that was solely attributable to the mining operations. Amax Coal Company v. Wyoming State Board of Equalization, 819 P.2d 825, 827 (Wyo. 1991).