# File lib/spreadsheet/workbook.rb, line 244
   def store_num_format(format, ifmt)
      record = 0x041E
      cch    = format.length
      length = 0x03 + cch

      header = [record, length].pack("vv")
      data   = [ifmt, cch].pack("vC")

      append(header, data, format)
   end