compare values and copy new values to clipboard

I need a macro which compares the values of the cells in two different sheets "A" and "B" and copies to the clipboard all cells which are in sheet "A" but not in sheet "B".

This macro needs to very efficient as I have a lot of data to compare !

also this has to be a macro approach and not formula if anybody was wondering..

could anyone help please?
thanks in advance
andy

i have got this code

Dim c As Range
Dim r As Range
Dim Book1_Range As Range
Dim i As Double
Dim sht1 As Worksheet
 
    Set Book1_Range = Sheets("Match").Range("M12:M1512") 
     
    For Each c In Sheets("Match").Range("N12:N1512") 'Range("N1512").End(xlUp)
        Set r = Book1_Range.Find(c, LookIn:=xlValue, lookat:=xlWhole, MatchCase:=True)
        If r Is Nothing Then
            i = i + 1
            Sheets("Match").Cells(i + 11, 28) = c.Value
        End If
         
    Next c

but i get an error "subscript out of range" in line
Set r = Book1_Range.Find(c, LookIn:=xlValue, lookat:=xlWhole, MatchCase:=True)

any ideas why ?
thankss

I'd try

Set r = Book1_Range.Find(What:=c.Value , LookIn:=xlValue, lookat:=xlWhole, MatchCase:=True)

i still get the same error message but thanks for the interest...