avoid retype the number more than one time withen acolumn

[Guest]

How can I avoid retyping the number more than one time withen acolumn.
I need a message "This no. already exist" to appear when I enter the same
number twice.
Thanks

 

[Jan Karel Pieterse]

Hi This,

How can I avoid retyping the number more than one time withen acolumn.
I need a message "This no. already exist" to appear when I enter the same
number twice.

Let's say you're in cel A1.

- Select the entire column by clicking the column letter.
- Choose Data, Validation from the menu.
- Click the dropdown next to "Allow" and select Custom.
- Type this formula in the box next to "Formula":
=COUNTIF(A1:$A$1,A1)=1
- Enter an error message and a prompt if you like and hit OK.

Regards,

Jan Karel Pieterse
Excel MVP
www.jkp-ads.com