Find Duplicate Entries

Got a workbook with 4 worksheets and sometimes we need to cut and paste a row from one worksheet to another, now thats easy now as we are all human and sometimes it gets copied and we have duplicate logs.

Now each sheet has usually not got that many rows in it, but that spreadsheet is getting sent to the highest people in the company and any mistakes look poor.

What i'm looking for is a way that i can highligh any rows that a duplicated in each worksheet. I can do it in each worksheet using conditional formatting with something like = COUNTIF($A8:$A$20,A8)>1. but don't know how to check that is not on any other worksheet. On every worksheet only need to check Col A for the duplicate information