Hi

Try
=IF(FREQUENCY(A10:A24,A10:A24)=1,"OK","R")

You can check unique list in 2 ways.

1 Worksheet formula
2 UDF (user defined function)

1 Worksheet Formula
Put this formula in cell A25
=IF(INT(COUNTA(A10:A24)/SUMPRODUCT(COUNTIF(A10:A24,A10:A24))),"OK","R")

2 UDF (User Defined Function)
Put below code in Module, and in cell A25 put this formula
=IF(isunique(A10:A24),"OK","R")

If not familiar with UDF, VBA and macros, see David McRitchie's site for
more on "getting started".

http://www.mvps.org/dmcritchie/excel/getstarted.htm

Function isUnique(rng As Range) As Boolean

    Dim myListCount, app As Application
    Set app = Application
    myListCount = app.CountA(rng)

    'use if condition to validate blank range
    'otherwise for blank range it shows error #Value!
    'if range is blank return 1=true or 0=false
    '1= list is uniqe
    '0=list is not uniqe

    'If myListCount = 0 Then
        'isUnique = 0 ' or 1     'Change to suit
        'Else
        isUnique = myListCount \ app.SumProduct(app.CountIf(rng, rng))
    'End If

End Function

Regards,
Shailesh Shah
http://in.geocities.com/shahshaileshs/
(Excel Add-ins Page)
If You Can't Excel with Talent, Triumph with Effort.

Keywords : check duplicate entery, repeat items,