And Yet More Stuff About Dual Units of Measure

If you add an item that uses dual measures to an order line and then submit the order, then you have to use dual measures for that item during fulfillment.
If you set up an item to use dual measures, and if you price it in the primary measure, then you can apply a coverage to the item. If you price it in the secondary, then you can't apply a coverage. See Set Up Coverages for Sales Orders.
If you need an orchestration process that does tasks that are specific for your dual measure item, then we recommend you use an assignment rule to assign that process instead of using line selection criteria. Also, you can use a dual measure attribute in your rule, such as Priced in Secondary UOM. See Guidelines for Assigning Orchestration Processes.
Order Management automatically calculates and sets the secondary quantity and the secondary measure on the order line according to your conversion rules. You can't manually modify these values on the order line.
You can't use dual units of measure with Reduce Inventory When a Sales Order Doesn't Require Picking or Shipping.
Make sure the setup for the item's secondary measure is identical in the item validation organization and in the organization that you use to fulfill the order line. If these measures aren't the same, the Order Management work area will display an error message that requests you to change the warehouse or cancel the order line.
You can set up rules for your item in the same way that you set them up when you don't use dual measures. For example, available-to-promise rules, sourcing rules, assignment sets, and so on in Global Ordering Promising.

If you use more than one measure to track the item:

You must set up a conversion between the primary measure and the secondary measure, and if
Your flow includes a purchase order or Advance Shipment Notice, then you must set up a conversion between the order line's measure and the purchase order's measure or the advance shipment notice's measure.

Primary and Secondary Quantity

You can substitute item x for another item y, but only if items x and y use the same primary measure and the same secondary measure. Order Management doesn't call pricing after the substitution so it expects the secondary shipped quantities to be in the same measure that you use for the original item.
If you apply a shipment tolerance on an order line, and if you price the item in the secondary measure, then the price on the invoice uses the secondary quantity that Order Management fulfilled, regardless of how you set the Quantity to Invoice for Overshipment parameter. See Manage Order Management Parameters.
If you revise an order, then you can't modify the secondary measure or the secondary ordered quantity on that revision.

Secondary UOM

You can't use the secondary UOM in some scenarios. You must use the primary UOM for these scenarios:

Model, such as an assemble-to-order item, pick-to-order item, or kit
Item that you can't ship, such as a subscription or coverage
Cost list or pricing guideline
Promising through Global Order Promising
Reserve inventory
Consign inventory
Outside processing
Contract manufacturing
Work order in discrete manufacturing
Global Trade Management
Field service
Service logistics

Order Management Extensions

You can use these attributes in an extension:

Secondary UOM
Secondary Quantity
Priced in Secondary UOM
Secondary Shipped Quantity
Secondary Fulfilled Quantity
Secondary RMA Delivered Quantity

Here's an example extension pseudocode:

If Priced in Secondary UOM is Yes, then set the value of an extensible flexfield on the order line.

You can only read these attributes. You can't update them.

See Attributes That You Can Use With Order Management Extensions.