If you click on the question mark in the top right corner you will get the definitions. More documentation is in the source code.

EDIT: As I say in the "warning" section of the readme file: usually it's not a good idea to show the raw data because it will confuse the end user. And if you add more explanation you will cause clutter and cognitive overload. I show the raw data mostly for people that want to dig into the source code.

On the topic of confusion, I think your demo would be clearer if you renamed "News stories bottom average score" to "Front page stories bottom average score". News is just a little too close to Newest, so I had to reread the definitions of both a couple of times. Cool project otherwise!

Actually, clicking anywhere on the graph will flip to the definitions, which is very bad UX.

Maybe think of it as two different graphs with the same x-axis, superimposed?

That's all this is really. The left Y axis applies to the sets that involve an average score, the right Y axis applies to pickup ratio only.

That said, what is a pickup ratio? Some sort of measure of extra votes over time?

Pickup ratio suppose to measure your chance of getting from "newest" page to the "news" page. But the more I think about it the more I'm inclined to think it's just a very hot topic detection device.

Pickup ratio > 1 means that the "newest" page has couple very interesting stories that are also seen on the "news" page.

Pickup ratio > 2 means that there is some sort of hysteria on HN about some particular topic ...