Depreciation allowance must be separately computed when particulars are furnished; absent particulars, no depreciation is allowed. If prescribed particulars have been furnished and depreciation claimed, the income should be estimated with gross profit assessed and deductions and allowances, including a separately worked out depreciation allowance, deducted; if net profit alone is estimated it must be subject to depreciation. If required particulars are not furnished and no depreciation claim is made, estimate income without allowing depreciation, note this exclusion in the assessment order, and retain the written down value of assets at the preceding year's level.