Changing code from Manual input to Calculated input

I have the below code, which updates the last entered value of column B into column D, when the value in column B is MANUALLY entered. I need it to update when a FORMULA changes the value, rather than a MANUAL input. I am a complete novice, so may you re-post the whole code with the changes, so that I can just copy and paste, please.

Thanks you so much.


Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False

If ColTo <> 0 Then
Cells(Target.Row, ColTo).Value = OldValue
Cells(Target.Row, ColTo + 1).Value = Date
End If

ColTo = 0
Application.EnableEvents = True

End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Count > 1 Then Exit Sub
Application.EnableEvents = False
OldValue = Target.Value
Select Case Target.Column
Case 2: ColTo = 4
Case 6: ColTo = 11
Case Else
End Select

Application.EnableEvents = True
End Sub