@Tut: On a related note, is there a way to change the order of columns on the sales invoice? I have added a custom field called “Item#” which now shows right after the description, but I would like it to show before the Item description.
@anaguib, please do not add unrelated questions to an existing post. That reduces your chance of getting an answer. Your post has been moved to a new topic, since it had nothing to do with due date references.
Assuming that by “Item#” you are referring to a line number on a document, the best way is not with a custom field, because that would have to be manually entered for each and every line on every transaction. Instead, use a custom theme. There is a Guide covering exactly this topic: https://www.manager.io/guides/10303.