I have made a few custom functions with VBA on a file I saved as an Add-in
with xla extension to make them available anywhere.

For example I included a simple function like:

Function MARGINE(Prezzo, Costo)
MARGINE = (Prezzo - Costo) / Prezzo
End Function

All functions work perfectly, but I would like to include the automatic tip
you have when you use standard built in functions.

To better explain, when you type =LEN( you see on top LEN(text) appearing.
Well, I would like the same to happen with my custom functions, I'd like the
suggestion to appear on the text bar on top: in this example I would like the
tip MARGINE(Prezzo,Costo) to appear on top.
How can I do this?
Nicola