automatically update a number in cell when template opens

[Guest]

I have just completed an invoice template for a new business, all works fine
but I am trying to insert a function which will automatically update a cell
number related to 'Invoice Number' each time I open the template so that I do
not have to keep trying to remember or search for the number of the last
invoice produced. Can this be done?

 

[Guest]

If your invoice number is in A1, for example, you could write a event macro
that updates the number each time the workbook is opened.

See

http://www.mvps.org/dmcritchie/excel/event.htm#wb_open