add my own graph to "Home"

[Denis Taranushin]

Hello.
I try to add my graph to home (like homepage screen
https://genieacs.com/images/screenshot.png)
But I can't understand how should I do it.
I edit  graphs.json.erb but have empty second graph

graphs.json.erb:
<%
threshold_green = (Time.now - (60 * 30))
threshold_yellow = (Time.now - (60 * 60 * 24))
%>
{
   "online_devices" : {
     "all_devices" : [
       {
         "label" : "Online now",
         "color" : "#5e5",
         "query" : {"_lastInform" : {"$gt" : "<%= threshold_green %>"}}
       },
       {
         "label" : "Past 24 hours",
         "color" : "#ee5",
         "query" : {"_lastInform" : {"$lt" : "<%= threshold_green %>", 
"$gt" : "<%= threshold_yellow %>"}}
       },
       {
         "label" : "Others",
         "color" : "#e55",
         "query" : {"_lastInform" : {"$lt" : "<%= threshold_yellow %>"}}
       }
     ],
      "devices" : [
       {
         "label" : "HG231f",
         "color" : "#5e5",
         "query" : {"_productClass" : "HG231f"}
       },
       {
         "label" : "DIR-615A",
         "color" : "#ee5",
         "query" : {"_productClass" : "DIR-615A"}
       },
       {
         "label" : "DIR_300A",
         "color" : "#e55",
         "query" : {"_productClass" : "DIR_300A"}
       }
     ]
   }
}



Please explane to me how does it work?
or may be someone shows me how to use Tags ("HG231f","DIR-615A", 
"DIR_300A") instead of "productClass"?