I'm a bit puzzled about the word "provisional" in AtCoder when I view my ratings.

Can anybody please explain how AtCoder rating system work?

At first I thought ten rated contests would "converge" my rating.

However that doesn't work.

There's a question mark next to my rating.

It says: "Your rating hasn't converged yet. Currently it's a little lower than your average performance."

Can anybody help me plz?