# File lib/mongrel/stats.rb, line 75
  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