# File temp/Graph/Plot.rb, line 205
      def field_width
        values = get_x_values
        max = @data.collect{|x| x[:data][X][-1]}.max
        dx = (max - values[-1]).to_f / (values[-1] - values[-2])
        (@graph_width.to_f - font_size*2*right_font) /
          (values.length + dx - right_align)
      end