Public Sub DiagonalSelection()
'Выделяет ячейки по диагонали выделенного диапазона
Dim i%, j%, n%
Dim mainDgnlFlg As Boolean
Dim dgnlRng As Range

      With ActiveWindow.RangeSelection
          'Главная диагональ
          mainDgnlFlg = Not (ActiveCell.Row = .Row Xor ActiveCell.Column = .Column)
          'n = Min(.Rows.Count, .Columns.Count)
          n = IIf(.Rows.Count < .Columns.Count, .Rows.Count, .Columns.Count)
          Set dgnlRng = .Cells(IIf(mainDgnlFlg, 1, .Rows.Count), 1)
          For j = 2 To n
              i = IIf(mainDgnlFlg, j, .Rows.Count + 1 - j)
              Set dgnlRng = Union(dgnlRng, .Cells(i, j))
          Next j
      End With 'ActiveWindow.RangeSelection
        
      dgnlRng.Select
        
End Sub