Restriction on unabsorbed depreciation and investment allowance reduces immediate deduction; remainder carried forward with extended absorption period. Restriction permits only two-thirds of unabsorbed depreciation and unabsorbed investment allowance to be deducted for the specified previous year; the balance of depreciation is added to the subsequent year's depreciation allowance and the balance of investment allowance is carried forward and absorbed in later years with the statutory carryforward period extendable until fully absorbed. The restriction is subject to a monetary threshold exemption and does not preclude application of other depreciation and investment allowance provisions where consistent. Shortfalls in tax due to this restriction are not subject to specified interest and penalty provisions if the shortfall is paid before filing the return.