The "piece picking confirmation" created for sales order picking, for example, should also work in the manual packing form.

This Would also improve the process, If you are using items with size/color/style. Because then, you have not to select the to pack size/Color/style in an additional dialog.

Suggested solution: Scan item bar code in the field "identifier". Then througt the unit conversion the right quantity/unit of measure is identified and is marked as packed.