Time stamp multiple cells changes when external database autorefreshes

[Breck]

I have a excel worksheet that is linked to a website. Every 60 minutes
the web query refreshes. 7500 rows of data in 4 columns is updated but
not all rows have changed since the last update.I found the following
code in the group that worked fine when I manually enter a number in
the forth column but when the web query refreshes the date it does not
create a time stamp

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column = 4 Then
Target.Offset(0, 10).Value = Now
'Or like this Format(Now, "mm/dd/yy hh:mm:ss") instead of Now
End If
End Sub

can this code be adjusted to create a time stamp when the web query
automatically refreshes every hour for only the rows that had changed
and not change the original date of the last change when the row
hasn't changed? Usually a row only changes one every 24 hours. But it
is possible that it may change more that once in 24 hours and it may
not change for more than a year. I hope that this isn't to difficult
an issue for a solution.

 

[Breck]

If possible I you also like to calculate the difference between the
old and the new values since the previous web query refresh. Thanks

 

[Breck]

If possible I you also like to calculate the difference between the
old and the new values since the previous web query refresh. Thanks

 

[Breck]

If possible I would also like to calculate the amount each cell
changes in column 4 since the last time it changed as the result of
the web query refresh.

 

[Breck]

If possible I would also like to calculate the amount each cell
changes in column 4 since the last time it changed as the result of
the web query refresh.