In PO detail entry, user enters an item and a quantity. The cost is pulled in from wherever it is supposed to pull in from. The extended cost is calculated (quantity * unit cost). The user overrides the extended cost to a different number to match the extended cost given by the vendor. Other software will recalculate the unit cost based on the new extended cost (new unit cost = new extended cost / quantity). Acumatica should treat the new unit cost as if the user keyed in a different price.