(a) Each utility shall so keep its accounts and records as to be able to furnish accurately and expeditiously statements of all transactions with associated companies, showing the general nature of the transactions, the amounts involved therein and the amounts included in each account prescribed herein with respect to such transactions.

(b) Dividends, rebates, or earnings from associated companies or mutual service companies representing refunds of the excess charges made by such companies over the cost to them, shall be cleared through account 1901, Charges by Associated Companies—Clearing, and shall be credited so far as practicable to the same accounts to which the corresponding charges were made, including proper distinction between construction and operating expenses. Credits applicable to operating expenses which it is impracticable to allocate among the accounts to which the corresponding charges have been made, shall be to account 1806, Duplicate Charges—Credit.