Export-oriented unit obligations govern duty-free imports, leasing, and a mandatory positive net foreign exchange requirement. EOU/EHTP/STP/BTP units undertaking to export their entire production (trading excluded) may import duty free inputs and capital goods, including second hand items, and may lease or sale and lease back capital goods subject to procedural safeguards. Units must maintain a positive Net Foreign Exchange (NFE) position computed in five year blocks; LoP/LoI authorises activities with specified validity and legal undertaking. DTA sales are permitted within prescribed ceilings and conditions, supplies to certain DTA recipients may count for NFE, and exit/conversion procedures require duty settlement or security and a 'No Dues Certificate'.