Question

The Challenge Checkers have a rating for difficulty. Does anyone know how this rating is derived?

Answer 1

I don't know the precise algorithm, but it's based on the number of cachers (particularly from that area, since automatic running of the checkers happens more for local cachers) who qualify compared to those who don't qualify. The less cachers who qualify, the higher the difficulty rating.

Comments

It's a pretty close guess of how it works. I will add a comment instead of "stealing" the answer.

By time, a challenge checker will be automatically run by most of Project-GC's paying members. That will give quite a few (thousands) of fullfilled/not fullfilled values.

These values are then combined into a rating. Those living close to the challenge will have a higher weight than those far away. In that way "local" challenges like "log 1000 finds in London" will not be considered close to impossible.