Reserve surcharge credit - If the customer has not yet returned the old unit but intends to do so in the near future then reserve surcharge credit should be chosen.
This will add both the new and old units to the WIP as above but the exchange unit will be added at a status of Reserve.
This will hold the WIP open until the old unit has been returned by the customer in order to issue a credit for the exchange part.
At a later stage if the unit has not been returned the part can be deleted from the WIP in order to close the WIP down.