Penalty calculation for registered firms: treat the registered as unregistered fiction only for tax computation, not total income. Penalty under section 271 is computed by reference to tax avoided; the fiction treating a registered firm as unregistered under section 271(2) is limited to tax computation and does not permit redetermination of the firm's total income. Annuity deposit, being deductible from total income and not from tax, is not to be deducted when applying the fiction for penalty calculation for a registered firm.