added :scale_by option for gauges

    #block = @@count_per_session_proc if unique?

    block = @@avg_per_session_proc if unique? && average?

    if block

    calc = if block

      instance_exec(_v, _t, &block)

    else

      _v

    end

    if calc && @opts[:scale_by]

      calc = calc.to_f * @opts[:scale_by].to_f

    end

    calc

  end

  def field_values_at(time, opts={}, &block)