The purchase order invoicing process has a functionality where the end user could identify a particular quantity which will be invoiced, and this could be controlled by the over/under deliver percentage on the purchase order line. The invoiced quantity in the purchase order invoice is linked to the item unit of measure, where the item inventory unit of measure could be different than the purchase unit of measure. For example a company stock specific item in Kilogram and purchase it from the vendor in Ton, in that sense the purchase invoice will be issued in tons, and the inventory will be added in kilogram and bear in mind that in some scenarios the inventory and purchase unit of measure are the same.
The unit of measures are defined on the item master, Product information management| Common| Released product, then press edit on a particular item record then go to Manage costs fast tab, as shown in the below screen shot the which illustrate the inventory base unit of measure.
In order identify the sales unit of measure move to Purchase fast tab
In a purchase order with quantity = 10 ea in a purchase line, the quantity here represented in the purchase unit of measure
The quantity of the purchase line which represents the purchase unit of measure will be reflected in the purchase order invoice, in addition to inventory unit of measure as well. The quantity in purchase unit of measure will be found under Lines details tab, Quantity filed. The quantity under update will be the base of the liability entry (Quantity * Purchase price).
The quantity in inventory unit of measure will be found under Product tab, Quantity filed.
If the user change the quantity in the quantity filed under the Line details tab, then the quantity under the Product tab will be changed as well, if the user change quantity under Product details the quantities under Line details tab will not change, in that said the changes mechanism only works in one way as mentioned.
If the second scenario of changes occurred where the user change quantities under Product tab, the system will keep the quantity under Line details tab as it represents the purchase unit of measure, which is acceptable if there is a slight differences in the purchase unit of measure and inventory unit of measure.
But if it is occurred without a business requirement this will lead to inconsistency between quantity in purchase order and quantity in inventory transaction.
The conclusion an issue may raise because of this mismatch, and in order to check the posted transactions, go to Accounts payable| Inquiry| Journals| Invoice journal then right click and press Record info, and press Show all fields.
The quantity in the left side represents quantity in purchase line, and quantity in right side represents the quantity updated in the inventory transactions.
The rationale behind it in case there is an item has two different unit of measure (Purchase & Inventory) and the user may want to change the quantity of which will be added to the inventory without changing the quantity in the purchase order, in the other hand if the item has the same unit of measure the quantities in the two fields should be identical, but if the user changes the quantities under line Product tab it will not change the quantities under Line details tab. Please note that the same mechanism working in the Sales order side.