An orders remaining quantity works similar to that of a contract.
Upon creation, every order is allocated a quantity and a quantity tolerance.
The remaining quantity is then calculated by taking the order quantity and adding the upper limit of the tolerance. For example a order with a quantity of 100 mt and a tolerance of 5 mt would have a remaining quantity of 105 mt.
As deliveries are allocated against the order, the remaining quantity will count down towards 0 mt.