The server does not automatically calculate the activity of every user every day. In order to average the top 100, it would have to calculate the activity of every user, so you might as well average all of them, no? Activity for past days is not stored, so yes it is more complicated than you think to graph it. I encourage you to go to get a hold of a copy of my activity hack off of vb.org and look over it to clear up your misconceptions.