This is where an underpayment can be made, once you have agreed the amount with Jeremy Broun. For example if there is a shortfall in postage to a distant zone or where a special deal has been agreed for numerous items and a cheaper total postage charge can be offered. The value entered is an example and is set each time by Jeremy Broun once the amount is agreed with/for a specific customer. So this facility should only be used as described here.