Duty payment timing: monthly duty must be remitted timely and attracts interest on outstanding amounts if unpaid. Monthly duty for notified goods must be paid within the prescribed monthly schedule and an intimation filed with the jurisdictional superintendent. Interest is payable on outstanding duty from the day after the due date until payment. Duty is recalculated on a pro rata basis for changes in machine operation, commencement or discontinuation of production at different retail sale prices, or revisions in duty rates; differential amounts are payable in the following cycle and overpayments refundable. Non declaration or contravention of declared factory plans attracts the duty rate for the highest retail sale price on all machines for the period, and continued operation after default results in duty based on the higher of declared or observed machines.