How can i stop same data being repeated in a column

[Ru]

I have a list of contract numbers relating to application numbers or
payments. they are in the format nnnnnnan or nnnnnnpn. The columns are fixed
to this format only. If they are entered with the a or p in the wrong place
or if they have been left out completely an error message will appear to
alert the user. I want to know how to alert the user if they enter an
application or a payment number that has already been entered.
ie if they enter 022079a4 but that same application has been entered else
where in the column.
Hope you can help
Ru

 

[papou]

Hello
See Chip Pearson's
http://www.cpearson.com/excel/duplicat.htm

HTH
Cordially
Pascal

 

[Ru]

Hi thanks for that link but i couldnt get it to work. If anyone has a step by
step suggestion that would be very helpful. And if its a formula should i put
it at the top of the column or where. All suggestions gratefully accepted.
Thanks
Ru

 

[Gord Dibben]

Try the Data Validation method at Chip's nodupe site.

http://www.cpearson.com/excel/NoDupEntry.htm


Gord Dibben Excel MVP