# File lib/barby/barcode/code_25.rb, line 106
    def checksum
      evens, odds = even_and_odd_digits
      sum = odds.inject(0){|sum,d| sum + d } + evens.inject(0){|sum,d| sum + (d*3) }
      sum %= 10
      sum.zero? ? 0 : 10-sum
    end