> I'm a developer and I am struggling to understand the reasoning behind that slider.
If you mean the 3 panel graphics then it seems pretty obvious. They want to focus attention on a small number of important things. They can change this slider once a month to give prominence to different things throughout the year.
If you mean the 3 panel graphics then it seems pretty obvious. They want to focus attention on a small number of important things. They can change this slider once a month to give prominence to different things throughout the year.