Chips has lots of stuff on duplicates, see www.cpearson.com

Hi Andy,
Please include the complete question in the text body,  one should
not be expected to look at the subject to understand the question
once the question is actually being viewed.

Conditional Formatting unfortunately cannot refer to another sheet,
but you can use a defined name for a reference and use that.
Select  Cell A1 on Sheet2  then place   sht2 into the name box.
as a shortcut to using    Insert, Name, Define, ...

Then select the area of interest on Sheet1  with cell A1 as the active cell.
Format, Conditional Formatting,
   Condition 1 Formula is:    =A1=OFFSET(sht2,ROW()-1,COLUMN()-1)

You might want to use a pattern color instead of using  Font, underscore
to try to underscore a empty cell.

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HTH,
David McRitchie, Microsoft MVP - Excel    [site changed  Nov. 2001]
My Excel Pages:  http://www.mvps.org/dmcritchie/excel/excel.htm
Search Page:        http://www.mvps.org/dmcritchie/excel/search.htm