WAN Quality Explanation

Hello community. I would like to know how does the WAN Quality feature works and from where does it get those latency values that are shown under the Status Tab → WAN Quality on the Balance web interface. I would like to have a clear understanding of this because I would like to explain something to one of our clients and I want to be prepared. Does these latency values come from analyzing the connection between our router and our ISP(in my case AT&T) or is it another way? Please explain that to me. Thanks in advance.

I have attached a picture of the router in question and sometimes it has spikes of 600ms in latency but right now is under 40ms. By the way the router is in the latest firmware available.

Have you find the explanation?
I have a Balance with 2 ISP and one is showing zero and the other graph like your


This is something I found in the forum regarding this issue.