Provisional assessment: importer must execute bond and provide bank guarantee or cash deposit; 20% deposit dispensed. Section 18 provisional assessment requires the importer to execute a prescribed bond to undertake payment of any deficiency between provisional and final duty and to furnish security as the proper officer deems fit; the Board dispensed with the 20% deposit rule and limited acceptable security to a bank guarantee or cash deposit (no sureties). The Board rescinded the 2011 Regulations and issued a uniform schedule setting security levels by importer class and nature of import, computed on duty differential, with Commissioner discretion to reduce security where justified.