If I enter -6.6 into a cell, Excel returns an error message saying that the formulae is incorrect. I am not trying to create a formulae. Just want to enter a negative number!
The cell is format as General. Have tried changing it to Number, but this did not help

How do I correct this?

Excel suggested putting an apostrophe before the number, e.g. '-6.6, but then I cannot reference this cell in a formulae in another cell