I have two answers for you:

1. the numbers are always entered in order a1,a2,a3,a4. In this case the
latest entered value is at the bottom of the column and the formula is:

=INDEX(A:A,MATCH(REPT("z",10),A:A,1),1)
will return the bottom value



2. the numbers are randomly updated. In this case you could use an event
macro:

Private Sub Worksheet_Change(ByVal Target As Range)
If Intersect(Range("A1:A5"), Target) Is Nothing Then
Else
Application.EnableEvents = False
Sheets("Sheet2").Range("A1").Value = Target.Value
Application.EnableEvents = True
End If
End Sub

or something similar.
--
Gary''s Student - gsnu200719