Using Looked-Up or Lookup in a portal
I have an "invoice" table and "invoice items" table that relate on an invoice number. In a layout showing the details of a single invoice, there is a portal of "invoice items" so the items are shown in a list.
When someone selects an item from the "invoice items" portal, I want the next field to autofill with the price of that item. At first I was going to create a script that had "If" for each item, followed by the price, but it seems like this would be a lot of unnecessary work. (There are many items.)
I found out about the Looked-Up Value option and that seems better. With that, would I simply create a third table ("Item prices" or something) and relate it to "Invoice items" by the item name?
Also, I see there is a calculated value option called "Lookup." Is this the same? Is there an advantage to using one over the other?