The E stands for expectancy. Yes this is a prediction, but the weatherforecast is a prediction as well and I still listen to it and wil react to that forecast.

So I do not understand were I am looking at the wrong side.

And yes I am still wondering how the PLE is calculated from what has happened. And in the question I did mention that the use of the system was continuous and stable, indicating the future is very similar to the past.

But maybe I should ask how long have the pages in the cache been there on average? (Half of the PLE?)

Thanks for participating,

Ben Brugman