Special audit powers allow Commissioner directed cost accountant audits when duty credit appears abnormal or fraudulent. Commissioner may require a manufacturer to have accounts audited by a nominated cost accountant where duty credit appears abnormal or obtained by fraud, collusion, willful misstatement or suppression; the nominee must submit a certified report within the period specified, expenses are fixed by the Commissioner and payable by the manufacturer and recoverable as sums due to the Government, and the manufacturer must be given an opportunity to be heard on audit-derived material proposed for use in proceedings; 'cost accountant' is defined by reference to the Cost and Works Accountants Act.