# File lib/spreadsheet/workbook.rb, line 255
   def store_date_system
      record = 0x0022
      length = 0x0002
      
      f1904 = 0
      f1904 = 1 if @date_system == 1904

      header = [record, length].pack("vv")
      data   = [f1904].pack("v")

      append(header, data)
   end