Based on the products being set to AVERAGE COST or LATEST COST and the tick boxes (In product defaults) set to update latest and average cost when goods are received.
When a Purchase Order is receipted and the Supplier Invoice is not present at the time, the 3 costs against the product, latest, average cost and the Suppliers latest cost, are all updated using that new Cost Price.
When the Supplier Invoice is subsequently received, the latest and Supplier latest cost are updated, but the average cost is NOT. The earlier transaction, the packing slip receipt, is also NOT updated with the new cost price.
Infusion have always said that the average cost can ONLY be updated at the time the goods are received, because that is the only point at which you know how many OLD / existing items you have at the OLD/ current average cost and can do the maths to calculate a new weighed average cost. At any point after that position, we cannot guarantee that stock quantities haven’t altered.
(ie existing quantity * existing average plus new quantity * new cost) = new total value – and that is divided by the total quantity to get the new average cost. )