Tonnage taxation restrictions limit loss carryforwards and disallow specified deductions while adjusting asset depreciation values. Tonnage income computation under the tonnage tax regime treats relevant deductions and allowances as if given effect in the relevant previous years, while prohibiting carry forward or set off of losses arising from operating qualifying ships and disallowing Chapter VI-A deductions for ship-operation profits. Written down value for assets used in the tonnage business is to be calculated as if depreciation had been claimed and allowed for the relevant prior years.