 That means that any residual book inventory quantity that may exist in the ERP system, assigned to the shop floor and to that specific HU is reported as consumed and issued to a distinct cost center.Inversely, should a workplace report a consumption from a HU that has no book inventory in the shop-floor stock (is already empty in the ERP system), an error is generated as a backlog in issuing the consumed materials, see chapter "Meaning of backflushing".What kind of unplanned transactions are used to handle this error is a question of internal policy of every firm.