N.H. Rev. Stat. Ann. § 374:13

When the commission has prescribed the form of accounts and records to be kept by public utilities of any class, each public utility of that class shall thereafter keep the accounts and records so prescribed accurately and honestly and in the manner prescribed; and it shall be unlawful for it to keep any other accounts or records covering the matters included in the accounts and records prescribed, except those which it may be required to keep by the authority of the United States or of any other state.