Assuming A1:A10 is the range of concern, give it the RangeName of "TheRange",
by highlighting it and doing Insert Name Define and typing "TheRange"
(without quotes) in the small upper box of the pop-up.

Then assuming B1 is the cell you wish to validate, click on it and do Data
Validation choose Custom in the Allow: window and in the Formula: window
type =COUNTIF(TheRange,B1)=1 and click OK

hth
Vaya con Dios,
Chuck, CABGx3



"gabch" wrote:


Hi,

How can I set the validation like this formula?
=countif(rngCheckColumn, CheckCelladdr)<=1


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