Adding Max/min lines to the area graph of light intensity

I was trying to add a max/min line to thew area graph which shows the light intensity. Can anyone tell me how to di it. The code below only plots the ldr area graph but not a line for the max value.
var areaGraph = new boltGraph();
var maxline = new boltGraph();
maxline.plotChart(“time_stamp” , 300);
areaGraph.plotChart(‘time_stamp’, ‘ldr’);

could you please explain the code you used line by line? it looks a little complicated.

@vinayak.joshi, could you pleasee share the code for this.