(1) Working papers shall show for the test period the overall cost of service per books for the filing public utility's utility operations during the test period, including allowances for return and income taxes based upon the rate of return claimed, together with the operating revenues of the filing public utility for the test period. If the filing public utility claims any adjustments to book figures, the cost of service based upon the claimed adjustments shall be shown on a separate schedule. If the amount of the filing public utility's total utility operating revenue differs significantly from its overall cost of service, including allowances for claimed return and income taxes, the filing public utility shall show the amounts available for return and taxes on income and return expressed as a percentage of rate base.