Each utility shall keep its books on a monthly basis, so that for each month all transactions applicable thereto, as nearly as may be ascertained, shall be entered in the books of the utility. A trial balance shall be taken after the monthly postings have been made, and each utility shall close its books at the end of each calendar year.
N.Y. Comp. Codes R. & Regs. Tit. 16 § 461.3