Prevent Duplicate Validation List Entries

My application has a form with 12 line items. Each line contains a column
(C13:C24) with a Validation > List (numbers 1-24). How do I prevent
duplicate numbers from being selected from the list?

TIA
Jim Kobzeff

Hello,

in the conditionnal format:
=countif($A$1:$A$1000;A1) >1
and place a color in the format for these cells
if you have 2 identiq cells, these 2 cells turn in color !
....Patrick


"JK" <JK@here.com> a écrit dans le message de news:
gEUvf.352$Xo5.302@trnddc02...
> My application has a form with 12 line items. Each line contains a column
> (C13:C24) with a Validation > List (numbers 1-24). How do I prevent
> duplicate numbers from being selected from the list?
>
> TIA
> Jim Kobzeff
>