What does it mean when I see ! in a formula?
This symbol will appear automatically when your formula links to another worksheet.
Eg If your formula reads = AberdeenSales!B8 then this is simply linking to the cell B8 in the spreadsheet called AberdeenSales.
You can do this by clicking on the cell in the first spreadsheet and typing = then simply go to and click in the cell B8 in the spreadsheet called AberdeenSales then press the Enter key. The formula reference AberdeenSales!B8 will automatically go into your formula.