# File lib/spreadsheet/excel/writer/workbook.rb, line 253
  def write_datemode workbook, writer
    mode = @date_base.year == 1899 ? 0x00 : 0x01
    data = [
      mode, # 0 = Base date is 1899-Dec-31
            #     (the cell value 1 represents 1900-Jan-01)
            # 1 = Base date is 1904-Jan-01
            #     (the cell value 1 represents 1904-Jan-02)
    ]
    write_op writer, 0x0022, data.pack('v')
  end