Pro rata customs duty on electricity from mixed imported and domestic coal: liability apportioned by the import/domestic coal ratio. Where a SEZ power unit uses a blend of imported and domestic coal, customs duty on electricity cleared to the DTA or non processing areas is chargeable on a pro rata basis corresponding to the proportion of imported coal in the fuel mix for the relevant period, by applying the duty rate for units using imported coal multiplied by the ratio of imported coal to total coal used during the period.