Each utility in Class A, Class B, or Class C shall keep its books on a monthly basis so that for each month all transactions applicable thereto shall be promptly carried to the general ledger. Each utility in Class D shall keep its books either on a monthly or quarterly basis. When a quarterly basis is used provisions contained herein relative to monthly entries shall be regarded as calling for quarterly entries. A trial balance shall be taken after the monthly or quarterly postings have been made, and each utility shall close its books as of the end of its fiscal year.
N.Y. Comp. Codes R. & Regs. Tit. 16 § 196.6