Add a Calculated field 'Unit Quantity On Hand' to sale order lines

The user changes the unit on a sales order from 'Each(1)' to 'Box(12)'. The 'Unit Quantity On Hand' field changes to show the quantity on hand in 'Box (12)  units on a sale order line. The primary stock on hand figure stays the same, being expressed in each units.

1. In the Navigation panel, click on Sales then click on Orders. 
2. Click on button New in the ribbon 
3. Add the Customer - in the drop down box
4. Add the Product by searching the Sales Order product you are looking for
5. Click on 'Unit' and you can choose from which Unit quantity you want (each or box) the Unit quantity on hand will automatically update itself