pool luck stats

[pajak666]

How to read that graph exactly?
the orange line tells that when mining on that pool actual difficulty for me was much higher than average?
are my assumptions correct?

[thep33t]

You are correct.

[pajak666]

comparing few pools graphs I've noticed that expected number of shares to find a block never goes below that value, that means that pool can't be extremely lucky and find and solve block quicker than usual?
that would mean that all mining calculators are inaccurate bc you will always have some harder days to solve a block with your pool? and none of ultra lucky days...