Invoice preparation under Rule 57GG: duplicate invoice required for Modvat credit and triplicate copy sent to Range Officer. Duplicate invoice copy remains the basis for claiming Modvat input credit; Rule 52A's duplicate-copy requirement continues to apply and is to be applied mutatis mutandis to registered persons under the new invoice provision. Registered persons must issue invoices in the prescribed proforma and forward the triplicate copy to the Range Officer for comparison. If Modvat is wrongly availed on the original copy, action may be taken under the Act and Rules.