You could use data validation. Select your range, in this case A1 - A100 then
data|validation|Custom

enter this formula

=COUNTIF($A$1:$A$100,A1)=1

Mike

"AdanaDarke" wrote:

I am using a workload log spreadsheet to enter individual customers names
daily as requests come in. To avoid entering customers twice by accident i
would like to know if there is any way to enter a customers name in a
formula, which will then search a column within the log and comeup with any
matches, so i can see if my entry is being duplicated.