So i've been doing quite a bit of research on PPC lately, and I have noticed that in Google Search, the #1 ad switches between different advertisers every time you refresh the page, and the same for every other spot. My question is, does anyone know how this ranking is determined? It seems that you can no longer aim for the #3 position (for example), but instead must aim for a range (maybe 2-5?) I've seen the ads jump around quite a bit so it seems like this range is pretty big. I assume that it's based on weighted percentages or something of that matter. Can anyone please elaborate on this? I would be more than happy to listen to you.