def set_x_axis(params)
    name, encoding = encode_utf16(params[:name], params[:name_encoding])
    formula = parse_series_formula(params[:name_formula])

    @x_axis_name     = name
    @x_axis_encoding = encoding
    @x_axis_formula  = formula
  end
def set_x_axis(params)
    name, encoding = encode_utf16(params[:name], params[:name_encoding])
    formula = parse_series_formula(params[:name_formula])

    @x_axis_name     = name
    @x_axis_encoding = encoding
    @x_axis_formula  = formula
  end
Set the properties of the X-axis.

 The set_x_axis() method is used to set properties of the X axis.

     chart.set_x_axis(:name => 'Sample length (m)' )

 The properties that can be set are:

     :name          (optional)
     :name_formula  (optional)

     * :name

       Set the name (title or caption) for the axis. The name is displayed
       below the X axis. This property is optional. The default is to have
       no axis name.

           chart.set_x_axis( :name => 'Sample length (m)' )

     * :name_formula

       Optional, can be used to link the name to a worksheet cell.
       See "Chart names and links".

           chart.set_x_axis(
             :name          => 'Sample length (m)',
             :name_formula  => '=Sheet1!$A$1'
           )

 Additional axis properties such as range, divisions and ticks will be made
 available in later releases.