Within a formula highlight a cell reference or the entire formula and press “F9”. This will then change the formula and show you the figures the result is based on rather than the cell references. See the picture below so you can see an example of this:
Be really careful with this! After you have used F9 to uncover what the formula is based on press ESC on your keyboard. ESC will return the formula to the cell. If you press ENTER on your keyboard the part or parts of the formula you have revealed will remain as the values. So in the example above, if you were to press ENTER after the second picture, the formula would be =A1+4 rather than =A1+B1.