At the end of each reporting period, a journal voucher shall be prepared charging the respective operating expense accounts and crediting the appropriate accrued accounts with the total of all accrued expenses. Items included in this category shall be expenses that have been incurred but for which payment is not due, such as electricity, gas, water, salaries, wages, etc. If the precise amount of the expense incurred with respect to these items cannot be determined, an estimate shall be made. This estimate may be made on the basis of meter readings, previous bills or payrolls. On the first day of the subsequent month this journal entry shall be reversed.