We can get "Sum of Quantity" for different documents like PO, Invoice, Proforma, etc.
[A] Go to "Settings" Module, Select "Document Field" under the Advanced settings.
[B] In Document field Select "Options" (1), Select the document from "Document Type" (2), Select "Buyer/Supplier" (3).
[C] Click on the grey mark (5) in front of "Sum of Quantity" (4) to make it blue, and click on "save". It will be on for the selected document and can be visible after saving the selected document.
Keywords: Sum of Quantity, PO, OC, Document field, Invoice, Options,