1. Add the Quote Line Quantity field to the Discount Schedule page layout.
2. Add your custom field to the Quote Line page layout.The custom field must be a formula field, number field, or a field that you can edit on the quote line record.
3. Add your custom field to the Quote Line Quantity picklist.
4. If you want to edit the custom field in the quote line editor, add the field to the quote line’s Line Editor field set.
5. Add the API name of your custom field to the Salesforce CPQ Advanced Calculator’s Custom Script object.