Compare values from two or more sheets, leave only non repeated values

Hi every, I'm need to build a macro or maybe using VBA a function to check if numbers are repeated between sheets in a Excel file. I have a first sheet called bl_db with 91543 rows, then in the same Excel I have another sheet called cm_db with 47285 rows and finally I have a third sheet called new_db with 853776 rows. All sheets can grow up with time. Then I need to add a macro to this Excel file and this macro should be executed every time those sheets are updated or by clicking a button in a four sheet where I must get results. So in the fourth sheet I should write only the numbers from new_db that is not in cm_db and bl_db, is that possible? Any help?

I read several docs:

• http://stackoverflow.com/questions/4...xcel-using-vba
• http://stackoverflow.com/questions/7...a-or-vsto-2005
• http://stackoverflow.com/questions/1...nt-in-2-sheets

But I'm not a VBA expert so I'm totally lost here