def initialize_defaults
      [:show_legend_key, :show_val, :show_cat_name, 
       :show_ser_name, :show_percent, :show_bubble_size, 
       :show_leader_lines].each do |attr|
        self.send("#{attr}=", false)
      end
    end
Initialize all the values to false as Excel requires them to
explicitly be disabled or all will show.