Acceptance of private records permits large excise taxpayers to use normal books instead of prescribed statutory formats. Factories meeting the high excise-payment threshold may elect to maintain their ordinary private books in lieu of prescribed statutory records, provided those records contain required information about production, materials and duty and are maintained with daily entries (unless otherwise permitted). The Commissioner may deem such private records proper and exempt the class from prior authentication; assessees must notify the Commissioner in writing identifying which private records replace each statutory record. Computerised records require monthly printed, serialised and bound copies, specified summary returns must still be submitted, and records must be preserved for a minimum period.