If the operation is a subcontracting operation and a purchase order number has been created for the operation (the purchase order number is created during printout), you can use this field to enter, change or delete the purchase order number. If you make changes in this field, for example delete the purchase order number, it will also affect other fields that belong to the subcontract. If you delete the purchase order number, the other fields that belong to the subcontract will be emptied and you cannot mark the order as Confirmed.