Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    If Target.Count > 1 Then Exit Sub
    
    On Error GoTo a
    If Target.Value = "up" Then
            tr = Target.Row
            tc = Target.Column
            Cells(tr - 1, tc) = Cells(tr - 1, tc) + Cells(tr + 1, tc)
            Cells(tr + 1, tc).Select
    End If
    If Target.Value = "down" Then
            tr = Target.Row
            tc = Target.Column
            Cells(tr - 3, tc) = Cells(tr - 3, tc) - Cells(tr - 1, tc)
            Cells(tr - 1, tc).Select
    End If
a:
End Sub