def set_size(params = {})
      @width    = params[:width]    if params[:width]
      @height   = params[:height]   if params[:height]
      @x_scale  = params[:x_scale]  if params[:x_scale]
      @y_scale  = params[:y_scale]  if params[:y_scale]
      @x_offset = params[:x_offset] if params[:x_offset]
      @y_offset = params[:y_offset] if params[:y_offset]
    end
def set_size(params = {})
      @width    = params[:width]    if params[:width]
      @height   = params[:height]   if params[:height]
      @x_scale  = params[:x_scale]  if params[:x_scale]
      @y_scale  = params[:y_scale]  if params[:y_scale]
      @x_offset = params[:x_offset] if params[:x_offset]
      @y_offset = params[:y_offset] if params[:y_offset]
    end
Set dimensions for scale for the chart.