How to prevent a certain value from being entered in a cell?

[bradewilk]

I need to prevent one certain value (specifically the #"24"only) from being entered in a cell. Would like to add an error message with correct entry instructions if someone attempts to enter that value if possible. Main thing is to prevent the entry though. Thanks.

 

[RedBeard]

Data validation: https://support.office.com/en-us/ar...to-cells-29fecbcc-d1b9-42c1-9d76-eff3ce5f7249