# File lib/spreadsheet/workbook.rb, line 59
   def calc_sheet_offsets
      offset = @datasize
      @worksheets.each{ |sheet|
         offset += BOF + sheet.name.length
      }

      offset += EOF

      @worksheets.each{ |sheet|
         sheet.offset = offset
         offset += sheet.datasize
      }

      @biffsize = offset
   end