You aren't stupid, but probably haven't encountered a streamgraph[1] before. It's just a stacked area graph where X is time (it's even labeled at the top) and Y

You aren't stupid, but probably haven't encountered a streamgraph[1] before. It's just a stacked area graph where X is time (it's even labeled at the top) and Y is frequency of calls (thickness, not from the origin). I think it's an excellent and informative graphic, personally. [1] http://www.leebyron.com/else/streamgraph/ http://www.leebyron.com/else/streamgraph/