How to set a variable as a cell value

How do I set a specific cell value as a variable on a worksheet to be declared throughout the workbook.

I am doing duty and VAT calculations and need to reference the cell for custom functions. As rates of Duty and VAT change I want anyone using the workbook to be able to change the value in the cell and therefore change the figures throughout the workbook.

Thanks

You can name one cell DUTY and another one VAT and use those names in place of cell references in formulas throughout the spreadsheet

Check help for names;defining for cells.

Click on the cell, Menue Data → Define Range…; In the window that pops up enter a name , e.g. VAT and click Add, OK.

Now you can use the Cell as VAT in all sheets.