how make Auto-Enter field with incremental number base on previous record
I apologise in advance for asking so basic question but I'm new in File Maker Pro and still find difficult how to use it.
I'm doing a simple "invoice" like database.
I have my "Inv_Number" (Numeric Filed) and I would like to have a kind of Auto-enter function that get the highest number used in "Inv_Number" + 1 so any time I make a new record I get the new number automatically.
I use to use the "Serial number" options in field option, but if you delete the latest record you won't get the right number anymore.
For my understanding in Auto-Enter I should use the "Calculate Value" option, but I don't know what/how function to use.