The Excel NOT function receives a logical value and simply returns the opposite logical value. I.e. if supplied with the value TRUE, the Not function returns FALSE and if supplied with the value FALSE, the function will return the value TRUE.
The syntax of the function is:
where the supplied logical argument can be supplied as a direct value, a value returned from another function, or as a reference to a cell containing a logical value.
Note that any numeric values, except zero are treated as the logical value TRUE, and the value zero is treated as the logical value FALSE.
The following spreadsheet shows examples of use of the Excel Not Function. The spreadsheet on the left shows the format of the functions and the spreadsheet on the right shows the results.
Formulas:

Results:

Further information and examples of the Excel Not function can be found on the Microsoft Office website.
If you get an error from the Excel Not function, this is likely to be the #VALUE! error:
#VALUE!    Occurs if the supplied argument is not a logical or numeric value. 