I have an spreadsheet column with merged cells. I would like to find a formula that would check the previous cell for a duplicate and return an error message. I have tried this formula"=COUNTIFs($A$1:$A$10001,$A1)<=1" but it does not work for merged cell. Please may I have help with coming up with a formula I can plug into Data vaildation scheme tha will not allow the same number to exist in a column of cells.
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