When the amount of any item affecting these accounts can not be accurately determined in time for inclusion in the accounts of the fiscal year in which the transaction occurs, the amount of the item shall be estimated and included in the proper accounts. When the item is audited the necessary adjustments shall be made through the accounts in which the estimate was recorded. If, during the interval between the date of inclusion of the item in the accounts and the date on which it is audited, a substantial difference from the initial estimate is determined, appropriate adjustments shall be made in the current accounts to cover such difference. The utility is not required to anticipate small items which would not appreciably affect these accounts.