# File rbSnack/tkSnackUtil.rb, line 348
    def plotBandWidth f1, b1, f2, b2, colour="#FBB"
       if @worldFrame[0]<f1 and f1<@worldFrame[2] and @worldFrame[1]<f2 and f2<@worldFrame[3]
          x1 = getX(f1-b1/2.0)
          x2 = getX(f1+b1/2.0)
          y1 = getY(f2-b2/2.0)
          y2 = getY(f2+b2/2.0)
          TkcOval.new(self,x1,y1,x2,y2){ fill colour} 
       end
    end