# File lib/mongrel/stats.rb, line 64
    def sd
      # (sqrt( ((s).sumsq - ( (s).sum * (s).sum / (s).n)) / ((s).n-1) ))
      begin
        return Math.sqrt( (@sumsq - ( @sum * @sum / @n)) / (@n-1) )
      rescue Errno::EDOM
        return 0.0
      end
    end