256.01-10—Billing procedures.
All invoices for services rendered to associate companies shall be submitted monthly with sufficient information and in sufficient detail to permit the associate company to identify and classify the charge in terms of the system of accounts prescribed by the regulatory authorities to which it is subject. Each month a statement shall be rendered to the associate company containing a summary of the accounts by work order by which the charges, classified as direct cost, indirect cost, and compensation for use of capital, can be entered in the accounts of the associate company.