Summary assessment power permits urgent revenue-protective assessments with prior supervisory permission; erroneous orders can be withdrawn on review. Section 64 permits the proper officer, with prior permission of the Additional Commissioner or Joint Commissioner, to make a summary assessment when evidence of tax liability emerges and delay may harm revenue; if the taxable person is unascertainable for a goods supply, the person in charge of the goods is deemed the taxable person liable. The supervisory officer may withdraw an erroneous summary order and require that the ordinary assessment and reassessment procedures be followed.