Determination of tax shortfall: notice and recovery require payment of tax, interest and penalty unless voluntary payment is made promptly. Determination of tax shortfall or wrongly availed input tax credit is initiated by a show cause notice requiring payment of tax, interest and penalty; a later statement may be deemed notice for additional periods if based on the same grounds. Voluntary payment before notice or promptly after a notice precludes service or avoids penalty for that tax; where payment is insufficient the proper officer issues an order determining tax, interest and penalty within the statutory limitation period.