Create articles and use them on invoice lines

Open Settings, section Invoices and letters, tab Articles (behind the toggle 2 more). Owners, admins and accountants can create, change and delete articles; a bookkeeper can create and change them but not delete; all other roles can open an article but only read it.
Choose New article and fill in Name, Article number (optional, but each number can be used once: This article number is already in use), Kind (Service or Material), Unit, Price entered as (net or gross), Unit price (in euros) and VAT rate (19 %, 7 % or 0 %). The name and a valid price are required. Choose Save.
To change an article, click its row, edit and choose Save. To remove it choose Delete and confirm with Yes, delete. If someone else saved the article in the meantime, the form says so; load the latest version and change it again.
On an invoice, add a line with the button Service or Material under the lines. On such a line the field Article lists the articles of the same kind, article number first, then the name. Pick one and the line takes over its name (as Description), its Unit and its VAT rate; choose No article to detach it. Custom line and Text lines have no article.
If you leave the unit price empty, the editor fills it in from the article once it has checked the draft. An article priced gross is converted to net on a net-priced invoice, and the other way round. Everything on the line can still be overwritten afterwards, including description, quantity, price and discount. The VAT rate is locked at 0 % when the invoice charges no VAT.
When the agent drafts an invoice it can look articles up by name or article number, so a well kept article list makes its drafts more exact.