Field help (PSH1PUU) 

This is the default purchase unit linked to the product. When the supplier is changed, this unit can be adjusted according to the purchase unit defined on the supplier-product record.
The product has two purchase units:

The purchase unit cannot be modified. A re-calculation of the quantities, prices and discounts is then carried out.
This unit is reused on the purchase order.

SEEINFO Upon invoicing of a product, the product PUR is used.

The unit is initialized by default to the purchase unit associated with the product. When an RFQ response has been taken into account, the unit specified in this response is submitted. When this field can be entered, a new unit can be selected in the unit table.